Everything would be so much more simple if he were dead. Let's say that Bob Dylan had passed away in his early to mid-thirties, as would have befitted the Christ-like figure his most fanatical admirers consider him to be. He would have released Blood On The Tracks in 1975, and completed Desire, the second masterpiece from his middle period, which appeared the following year. Disciples would never have had to struggle with his distinctive readings of songs such as "Froggie Went A-Courtin'", "The Little Drummer Boy", or "Here Comes Santa Claus". They would have been spared the need to follow him to places like Bournemouth, Limoges and Spokane, to hear him revisit his classic compositions in a voice that, on a bad night, has the timbre of a cracked bell.

The fog of secrecy that surrounds his life would long since have lifted.

There would have been little point in devoted admirers rehearsing, as so many have, questions he might answer concerning his lyrics. "When you wrote that line, Bob, about 40 red, white and blue shoe strings, did you mean 40 striped laces, or 13 red, 13 white and 14 blue?" And did you really have a job in the great north woods [as you wrote in 'Tangled Up In Blue'] 'working as a cook for a spell'? What were the specials? Who was your sous chef?" And - this next question was actually put to him by his former Boswell and occasional collaborator, Larry "Ratso" Sloman, concerning Dylan's sublime 1966 love song "Sad Eyed Lady Of The Lowlands" - "In the chorus, 'My warehouse eyes, my Arabian drums'... That word, 'eyes'. What is it? A noun, or a verb?

The constant need to explain his work - a curse Bob Dylan has bemoaned for 50 years - would be over, as would the need to avoid the attentions of his more unhinged fans. Gone, too, all those fatiguing enquiries concerning his alleged lovers, opiate use and undignified stories such as those recent reports about neighbours to his main residence, in Malibu, complaining about the odour emanating from his workers' Portaloos, with predictable headlines such as "Blowin' In The Wind". On a superficial level, at least, everybody wins.

Dylan, though, remains obstinately fit and industrious, and celebrates his 70th birthday in May. In 2006, after a frustratingly inconsistent run of albums over the previous three decades (disappointing enough at certain points, such as his "born-again" period in the early Eighties, to convince some that his talent had deserted him forever) he produced the triumphant Modern Times. It's the best thing he's done, I suggested to one of his compatriots (a household name who, like many I interviewed for this article, insisted on remaining anonymous) since Desire. "It's the best thing he's done," came the reply, "since Blood On The Tracks." That renaissance has been sustained with 2009's

Together Through Life. And in recent years - having already proved himself the greatest folk singer, lyricist and rock'n'roll artist of all time - the famously taciturn performer has improbably evolved into the world's greatest-ever DJ as the avuncular host of the arcane, witty and magnificent series

Theme Time Radio Hour. "Critics are notoriously liberal with their use of the term 'genius'," says fellow songwriter Steve Earle. "Bob Dylan is one of the very few people in the history of popular music who you can unquestionably apply that word to. From the moment Dylan arrived as a songwriter, he was [so] much better than everybody else around

[just like], to take a crude example, Pelé was at his peak, or Tiger Woods. He emerged from nowhere, like an alien. And that was just the start." "Hang on," I say. "Aren't you the man who claimed that Townes Van Zandt is the greatest songwriter in the history of popular music, 'And I'll stand on Bob Dylan's coffee table in my cowboy boots and say that'?" "This may sound a bit odd," the Texan replies, "but I was comparatively late in understanding Bob Dylan's overwhelming importance as a songwriter. Everybody who does my job exists in the shadow of Bob Dylan. There are two categories: Dylan and everybody else. It's as simple as that. And it's going to be that way until he dies."

It could be that, because you have somehow grown up beyond the reach of English- speaking popular culture - you are now asking: who exactly is Bob Dylan? On a literal level, the question is a straightforward one. Born Robert Zimmerman on 24 May 1941, in Duluth, Minnesota, he first used his new name in 1960 and emerged as an unrivalled talent in the New York folk clubs. Most agree that he has enjoyed three especially brilliant periods: first as an acoustic artist, with protest anthems such as "The Times They are A-Changin'", in the early Sixties; then with his great electric trilogy, Bringing It All Back Home, Highway 61 Revisited and Blonde On Blonde, in the middle years of that decade; and finally the more introspective work of his

Blood On The Tracks period in the mid-Seventies. Fans argue as to just when his current, fourth great flowering began, but there's a broad consensus that, in the studio at least, it is ongoing.

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His voice may, like the Havana cigars and bourbon to which it is often lazily compared, be an acquired taste, but Dylan is responsible, as much as Billie Holiday, for reinventing the whole style of popular singing. The idea that, even now his vocal range has been significantly reduced, Bob Dylan "can't sing" is simply wrong. In the words of his friend Bono: "Almost no one sings like Elvis Presley any more.

Hundreds try to sing like Dylan. To understand his impact as a singer, you have to imagine a world without Tom Waits, Kurt Cobain, Bruce Springsteen, Lucinda Williams or any other vocalist with a cracked voice, dirt-bowl yelp or bluesy street howl."

For a journalist, the world of Dylan is not exactly the most comfortable to inhabit. In a landscape famous for its uncertainties, one thing is terribly clear: the subject himself doesn't want you anywhere near him. It's true that there are individuals who are more reclusive - astronaut Neil Armstrong, or author Thomas Pynchon spring to mind - but generally speaking those people have the decency never to go out. Dylan, meanwhile, circles the globe on his so-called Never Ending Tour. While researching this article, travelling across Europe and America, watching his shows and interviewing musicians, one question kept recurring. What kind of hermit is it who won't stay in his cave?

The closer anybody is to Bob Dylan, the less enthusiasm they have for speaking about him. It's no exaggeration to say that something akin to the Mafia tradition of omertà surrounds him. Elvis Costello, who has toured with Dylan, agreed to cooperate with this article only if his contribution was drawn from an on-the-record e-mail exchange. One source who's known Bob Dylan for many years was quite happy to tell me, in some detail, about how he'd been arrested for punching his wife. When Bob Dylan's name came up, though, his mood altered. "You don't talk about Bob," he said. "That's the rule."

Dylan's manager Jeff Rosen remained a helpful contact; if I wanted to see a concert in London or Marseille, I knew that when I got to the venue, tickets would be waiting. But he made two things clear from the start, namely that, "I never talk about Mr Dylan," and, "Mr Dylan doesn't give press interviews."

This last statement, as aficionados will know, is only intermittently true, even though the nearest I will get to Dylan is being put through to someone who has him on their other phone line.

In the mid-Nineties, I spent a couple of days interviewing Allen Ginsberg at his apartment in New York. "You wanna talk to anyone else?" Ginsberg asked. "Burroughs? Corso? Dylan?"

Ginsberg dialled the calls. The first two writers spoke to me, even if, in poet Gregory Corso's case, what he said was barely recognisable as English. The third call rang out. Ginsberg left a message which, he assured me later, was eventually returned.

Bob Dylan has become incrementally trickier to reach in recent years, though he will very rarely emerge, rather in the way that God occasionally appears to Portuguese virgins. Dylan, on the other hand, usually manifests himself in the presence of representatives of Rolling Stone magazine (which judged his 1965 classic "Like A Rolling Stone" to be the greatest song of the 20th century). At the time of writing, he last surfaced in its pages two years ago, when he spoke to Hunter S Thompson's authorised biographer, Douglas Brinkley.

As is mandatory, that conversation broached none of the more sensitive areas a subject might normally discuss with an interviewer, though the singer did make a few fascinating observations, notably in relation to a meeting with Nicolas Sarkozy. "It was like looking at my mirror image," Bob Dylan said - a surprising remark, given Sarkozy's undistinguished record in certain areas: I'm thinking mainly of things like truth, dignity, tact, aggression towards strangers, intimidation of the media, marital fidelity, connivance with big business and loyalty to friends whose success might impede his own self-advancement. "I can see," Dylan enthused, "why he is the head of France." Sarkozy, he went on, is "warm and extremely likeable". ("In exactly the same way," you expect the singer to conclude, "that I am.")

In terms of Dylan's recent history with the press, examples of such affability are elusive. The last interviewer who attempted to address Dylan like a normal human being was Andy Kershaw, on The Old Grey Whistle Test in November 1985, a gesture unreciprocated by his guest who terminated what was an excruciating if memorable collision.

Such temerity is rare, as my friend the Portland cartoonist John Callahan once told me. Dylan was one of the few stars with the curiosity to have sought out Callahan's work (the level of taste in the quadriplegic's art is typified by the title of his autobiography: Don't Worry, He Won't Get Far On Foot). "He met me backstage," said Callahan, who died last year. "I steered my wheelchair towards him. He said, 'Hallo.' And I found myself saying, 'I write songs, too.' That's like meeting Jesus Christ and telling him: 'I, too, have suffered at the hands of mine enemies.'"

On the whole, trying to talk to Bob Dylan is a bit like trying to talk to Jesus, with the important difference that prayer won't help you. And, as with Jesus, we each have our own personal relationship with Bob. My own is coloured by the fact that I live in Crouch End, an area of north London he used to explore fairly regularly. I've never met Dylan, but the guy who runs my local Indian has. So has the barmaid in my local, and a lady who sold a house two streets away from me. (The eventual purchaser was GQ restaurant reviewer Simon Kelner.) The vendor saw, "this Jewish guy on the doorstep. He said: 'Don't change the taps.' The fittings were garish, styled in what the less politically correct would call "Saudi gold". Dylan pulled out of the deal when he found himself on the front page of the Hornsey Journal. The table opposite me at Banners Cafe, where I'm correcting this on a laptop, has a brass plaque that reads " Bob Dylan Sat Here, 1993".

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His legendary disdain for the media inspired a play by writer Janey Preger, Bobby Wants To Meet Me. Broadcast on BBC2 in 1981, its main character was Neville Morris, a Mancunian journalist and Dylan obsessive who has been hoaxed into believing he has an interview with the singer. It's Neville who invented that question about the multicoloured shoestrings, as part of his rehearsal to impress the artist. "I'll tell him I'm an orphan," Morris says. "My mother was Spanish. She was knifed by a jealous lover. I never knew my father but I was told he was a piano player. I was brought up by Moldovan horse traders. I travelled across Europe on horseback to Hamburg, where I hung out with a junkie stripper. I went to Greece where I lived on the street..." "Hang on," his girlfriend asks. "How did you learn English?" "Salford Technical College," a friend mutters.

In Marseille, a few days after I began my pilgrimage in June last year, the atmosphere in the lobby of Le Dôme is like Wembley before the FA Cup final. There's a surprising mix of ages; many of the crowd are far too young to have seen Dylan perform in the early Nineties. His live shows weren't at their most consistent back then: one musician who played on those tours told me that he'd twice fallen asleep on stage with Dylan. I went to one London concert around that time with a long-standing fan who left after 20 minutes because Dylan's performance had reduced him to tears. The singer came on looking as if he'd just been hit over the head with a baseball bat. And Dylan, as I told Bucky Baxter (the guitarist credited with reinventing Bob Dylan's sound in the Nineties) appeared to be playing practical jokes on his band for his own amusement. "He did do that," Baxter said. "One night around that time, at Hammersmith, he was about to go into [his 1963 classic] 'Don't Think Twice, It's Alright'. He said, 'Hey, Bucky! Play mandolin on this.' I am not really a mandolin player; I could only play in certain keys. Halfway through, he stops the band, turns to the audience and points to me. He says: 'He isn't playing, he's miming.' And then: 'Should I fire him?' The whole audience yells,

'Yeah!' I went to see him afterwards. I was really p***ed off. He said: 'Forget it - I was just foolin' with ya.'"

Marseille, like the other dates I've seen on this tour, is different. True, Dylan, whose guitar-playing is rumoured to be restricted by arthritis, stands at his keyboard, at an oblique angle to an audience he does not trouble to acknowledge. He looks, as Joan Baez puts it, "as though he'd rather be in a dark parlour, playing chess; perhaps in a sense he is."

These days, Dylan has guitarist Charlie Sexton in the band, and while the singer may radiate indifference, Sexton, always a dynamic and compelling musician, is allowed to take centre stage. As a group performance it's extraordinary, and that, you feel, is how Dylan wants to appear: as a guy in the band. Sexton, who learned the basics of boxing in the Eighties under coach Bruce "the Mouse"

Strauss, and still works out on the road, looks in far better shape than he did 15 years ago.

In the front rows, I notice several faces who were at Nice the night before. They punch the air, tweeting the names of songs, four or five bars in. Matt, from County Durham, tells me he's saved up all year in order to spend his holiday following Dylan around. "What did you think?" I ask him, on the shuttle bus back into town. "Great. Fing great." "Were you at the show last night?" "Nice? Yes. Fing great, wasn't it?" "What did you think of Lyon?" "Lyon? Lyon was fing great. Every night," Matt says, "is fing great."

The next day I meet Matt at the airport, which is closed. He's looking to hitch a ride. "I have to get to Barcelona. How long will that take by road?" "Barcelona? Why?" "What do you mean, why?" He gives me the kind of look a member of the Inquisition might give someone who's carrying the Koran. "You mean, you're not going?"

There is a side to some Bob Dylan fans that can, frankly, be unnerving, as I suggested to Mitch Blank, who I met in his Greenwich Village apartment. Blank, a grey-haired man in his sixties, is the semi-official archivist for Dylan's office. Blank is thanked as "hypnotist collector" on credits for things like the 2005 Scorsese Arena documentary No Direction Home (which Dylan maintains he's never seen; his only involvement with the project were the ten hours of interviews he recorded with manager Rosen). Blank's flat is full of Dylan memorabilia and thousands of hours of recordings. He has 9,000 open-reel tapes stored across the state line. Blank has spent recent days rescuing albums from the fire-damaged property of a deceased collector whose body had only recently been removed from the apartment, an exercise that required arc lights, masks and a dozen assistants. The smell, he says, was "horrendous".

He shows me part of the case from the piano photographed on the cover of Dylan's 1975 studio album The Basement Tapes.

Dylanologists, Blank says, come from all over the world. "They often ask if they can take a screw from the piano. It has become," he explains, "mythological." "Like the true cross?" "Right." "What happens when they take a screw?" "I let them." "What if you run out?" "I go to the hardware store and buy more. They leave happy."

Years ago, Blank received a call from a fan. "He said: 'Mitch, Bob was here. He smoked a pack of cigarettes. He's left the butts. You want one?'"

Blank asked why he'd want a cigarette end. "In the future they say they'll be able to clone people from DNA. That means you can have your own Bob Dylan."

There is, Blank tells me, "a point where you have to draw the line".

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Blank, who has a day job, is well-balanced. But there was an incident when I was leaving another Dylanologist's house. He stopped me and mentioned another collector. "Listen," he said. "This guy is crazy. If anything happens to me... Well, remember, tell the police that the guy who did it was... [name and address supplied]."

How on earth, you find yourself asking, did adulation for a Minnesota shopkeeper's son become so intense? Some years ago, at a retirement home in Phoenix, Arizona, I interviewed an elderly lady who'd been a friend of Beatty, Dylan's mother, in Hibbing, Minnesota. "Such a sweet boy," she told me. "He played in my yard. Well-behaved. A little shy."

Back in London, I spoke to Philip Saville, the director responsible for, among other things, Alan Bleasdale's Boys From The Blackstuff. Saville directed The Madhouse On Castle Street, a BBC TV play transmitted in January 1963, now destroyed, itself the subject of an Arena documentary six years ago. "I was in New York in 1961," Saville told me. "I used to go to this music club; you'd meet WH Auden there, people like that. One night, this young man came on with a mouth organ and guitar. He was relatively unknown, then. I thought he was extraordinary."

Back in London, Saville recalls, "we were working on Madhouse, an Evan Jones play. I said, 'I'd love to get Bob Dylan for this.' I flew back to New York and we brought him over, with his manager Albert Grossman."

Saville put Dylan in the May Fair Hotel, where he was thrown out for smoking weed. "My wife and I had a house in Hampstead. He came to stay with us." Saville found Dylan sitting on the landing one day, singing "Blowin' In The Wind" to the au pairs. "This," he says, "was long before it was even recorded." "What was he like back then?" "I adored him. He spent a lot of time in art galleries. Very forthright in his beliefs," says Saville, referring to Dylan's democratic libertarianism, "though he wasn't a political animal, even then." (Years later, even George W Bush, a man who might have politicised anybody, would fail to elicit condemnation from Dylan.) "Approachable?" "He didn't talk a lot. But people who say very little, especially if they pause, come across as more profound than they really are."

Abram Zimmerman, Bob's father, ran a hardware store. His son adopted his new surname while in college at Minneapolis (almost certainly out of affection for Dylan Thomas). He was just 20 when Saville brought him over to London and still in thrall to his first great influence, Woody Guthrie, the Oklahoma folksinger whose Midwest accent and vagrant history he did his best to mimic.

As late as October 1964, Dylan would be telling the distinguished critic Nat Hentoff - usually nobody's fool - that, as Hentoff wrote in the New Yorker: "He ran away from home seven times - at ten, at 12, at 13, at 15, at 15-and-a-half, at 17 and at 18. His travels took in South Dakota, New Mexico, Kansas and California." "Did he lie about his past?" I ask Saville. "No," the director says. "He never claimed to be anything other than what he was: a nice, polite, middle-class Jewish boy."

Philip Saville's recollections are in marked contrast to the tone of others who met him in England around this time. There are more than a thousand books relating solely, or in significant part, to Bob Dylan. One of the best is David Hadju's Positively 4th Street, which follows the young singer's relationship with Joan Baez, as well as with her sister Mimi and her husband, writer Richard Fariña, who died in a motorbike accident in April 1966.

Dylan does not emerge as an especially sympathetic figure; the many reverses he experienced in the battle to maintain monogamous relationships are recounted by Hadju and numerous other biographers, and alluded to rather more forgivingly in his own 2004 memoir, Chronicles: Volume One. He is pictured on the cover of The Freewheelin' Bob Dylan arm-in-arm with then girlfriend Suze Rotolo who, Dylan writes, "had a smile that could light up a street full of people" [not literally, of course, that would be hazardous]. He left Rotolo for Baez who, already a major star, made Dylan her lover and protégé. According to Baez, when Dylan told her he was leaving her to marry Sara Lownds,"I didn't even know there was a Sara."

Bob Dylan is known to have been married twice: to Sara (1965-1977) and to backing singer Carolyn Dennis (1986-1992). There have been a number of other significant girlfriends. He has four grown-up children from his marriage to Sara: Jesse, Anna Lea, Samuel and Jakob, and a daughter, Desiree, from his marriage to Carolyn.

Dylan shared certain failings with fellow dandy Oscar Wilde: a propensity for occasional dissembling, minor plagiarism, reckless intoxication, infidelity and a sometimes cruel edge to his caustic wit, but with Dylan, as with Wilde, these sins are, if not excused, then brilliantly outshone by the work.

There are other songwriters of his age whose legacy will endure: Randy Newman and Leonard Cohen prime among them. But whereas their work - however brilliant - has a polished, fundamentally orthodox quality, Dylan, at his stunning best, seems to be in touch with another reality.

In Venice Beach, Los Angeles, I met Bruce Langhorne. Bruce played guitar for Dylan as early as Freewheelin' and was a regular collaborator up to and including Pat Garrett And Billy The Kid in 1973. He plays on "Like A Rolling Stone" and was the inspiration for, and played on, "Mr Tambourine Man", which Dylan wrote after seeing Langhorne at a party, playing a large Turkish drum. ("If you had Bruce with you," Dylan remarked, "that's all you would need to do just about anything.") "When I first heard Bobby," said Langhorne, "I wasn't that impressed by his voice. Not at first. But he turned out to be extraordinary. He worked in a way that was very different from anything I'd ever experienced. The connection I had with Bobby was telepathic, and when I use that word, I mean it. I played on every song on Bringing It All Back Home. Some of those numbers were done in one or two takes. Everything with Bob was intuitive."

Bruce shows me his copy of Chronicles. It's carefully inscribed, in the author's hand: "To Bruce. It was better to be in chains with friends than in a garden with strangers. [An ancient Persian proverb.] "So true, huh? From Bob Dylan to Bruce: Mr Tambourine Man."

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Given Dylan's secretive nature, hearing that he was going to publish a memoir in 2004 felt a bit like being told that Lord Lucan would be next week's guest on Desert Island Discs. One distinguished British writer reviewed Chronicles as follows: "If you are not weeping with gratitude by the end, then frankly the age has passed you by." I've read Chronicles six times now, and my handkerchief is still dry. I suspect the reviewer delivered this glowing endorsement in order to get his name on the cover of the paperback, and consequently must have been weeping for a second time when that edition finally appeared, and he found he had been out-grovelled by a man from the Daily Telegraph.

Chronicles makes for fascinating reading but is extraordinarily devoid of emotion; very like Scorsese's No Direction Home, it is compelling in terms of musicology and folk history but, biographically speaking, a masterclass in the art of non-disclosure. Even his most fundamental relationships are blurred: Dylan mischievously refers to his spouse throughout Chronicles only as "my wife", making it impossible, in some passages, to know which one he's referring to.

But how can you not forgive the man who wrote the following paragraph? "The waitress came over and said, 'How about eating?' I looked at the menu then I looked at my wife. The one thing about her that I always loved was that she was never one of those people who thinks that someone else is the answer to their happiness. She has always had her own built-in happiness. I valued her opinion, and I trusted her. 'You order,' I said."

Even Joan Baez, who was betrayed by Dylan on a number of levels, and who complains that he was "rarely tender and seldom reached out to anticipate another's needs", acknowledges that "his humour was dry and splendid". Dylan toured Britain in both 1965 and 1966. On the latter tour, ardent traditionalist John Cordwell, enraged by Dylan's second, amplified half of the set at Manchester Free Trade Hall, famously shouted "Judas!" at the singer. (This one critical moment in pop history is celebrated in two documentary studies: Like The Night, a tremendous book by CP Lee, and Ghosts Of Electricity, a 1999 BBC Radio 3 documentary made by Andy Kershaw.)

In 1965, Dylan had been greeted by a national press who patronised him on the basis that a pop singer must, by definition, be less intelligent than they were: an assumption which, in Dylan's case, proved dangerous.

One of the many bizarre press conferences on that tour, captured in DA Pennebaker's magnificent documentary, Don't Look Back, is exquisitely reprised by Cate Blanchett, who gives a stunning performance as Dylan in Todd Haynes' 2007 movie, I'm Not There.

Reporter: "How many people who major in the same musical vineyard in which you toil are protest singers? That is, people who use their music to protest the social state in which we live today?"

Dylan: "How many?"

Reporter: "Yes. How many?"

Dylan: "I think there are about 136."

Reporter: "About 136, or exactly 136?"

Dylan: "It's either 136 or 142."

You know something?" Bruce Langhorne had told me. "I have always believed that fame is a curse. I never envied one of the famous people I've known." "None of them?" "Not one."

In July 1966, Bob Dylan came off his motorcycle near his family home at Bearsville, close to Woodstock in upstate New York: an accident (three months almost to the day after Fariña's) thought to have been exaggerated by the singer in order to escape the pressures of touring. Ever since then, he has struggled to keep his distance from his huge and obsessed fanbase. His elusiveness has, naturally enough, only increased their inquisitiveness.

Dylan moved out of Bearsville after the 1969 Woodstock festival, complaining that his house was besieged by "druggies". He moved to Greenwich Village, where he bought a property uncomfortably close to the HQ of his Moriarty, AJ Weberman. Weberman was the embodiment of everything Bob Dylan was striving to avoid: an invasive fan who saw him as an oracle, and was maniacally dedicated to propelling Dylan back into the spotlight.

Weberman, self-proclaimed inventor of the science of "garbology", rooted through Dylan's bins in the early Seventies.

For reasons that are still hard to explain, Dylan let himself be taped speaking on the phone to Weberman in January 1971. The bizarre recording is still commercially available. AJ harangues him for his sluggishness in opposing the Vietnam War. One exchange goes as follows...

Dylan: "I think I'm going to write a song about you."

Weberman: "I could use the publicity. What's it called?"

Dylan: "Pig."

AJ Weberman now lives in a comfortable apartment in Manhattan, purchased with proceeds whose source he has never sought to conceal. I meet him for tea at the Yippie Museum and Café in Bleecker Street. For a while we are joined by his fellow counterculture activist, Dana Beal. A few months later, I turn on the news to see that Dana has been apprehended on Highway 6, Ashland, Nebraska, in a van found to contain 186lb of marijuana. AJ will post on Facebook that this cargo (which weighs far more than he does) was for "Dana's personal use".

Talking to AJ Weberman, you quickly sense how wrong it is to accuse Dylan of being paranoid about securing his privacy. Many of his fans can be over-defensive of him: the screenwriter Mark Jacobson, reviewing Dylan's interminable 1978 movie Renaldo And Clara, disliked the movie to the point that he actually wished the singer dead in print: a remark which, Jacobson tells me, provoked messages causing him to fear for his safety.

Weberman, you sense, is not so much a man on the road to madness, as someone who has arrived there, bought a property and is renting out rooms. Many of Dylan's songs are, in AJ's opinion, coded attacks on him. Others, as he claims in his incredibly libellous book RightWing Bob, are about Dylan's supposed experience in relation to heroin, HIV and racism.

This is Al on "Blowin' In The Wind": "'How many roads?' That's a reference to Cecil Rhodes [the English-born founder of Rhodesia]. Dylan means how long before you realise blacks are nothing but manservants. Why a white dove? This song asks, 'How long before apartheid is going to work in America?'

The answer is 'blowin' in the wind'. That means, hang the niggers from the trees."

The day Dylan beat him up, Weberman says it felt like a privilege. "I'd been going though his trash. He knocked me down. I was glad to see him, even though he was banging my head against the sidewalk. Afterwards these bums come over and say, 'Did he get much money?' I say, 'Money'? That was Bob Dylan.'"

At one point I mention a relatively obscure Dylan composition called "Sign Language". "Now that," I suggest, "really is a bad song."

Weberman looks appalled. "Are you crazy? Bob has never written a bad song. Bob Dylan," he adds, with some warmth, "is a genius."

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Why would so secretive a man keep touring, and expose himself to huge audiences every year? It's not the money, colleagues say.

Dylan is believed to own around a dozen properties, all over the world.

The singer himself has given various explanations, ranging from the clichéd ("It's in my blood") to the bizarre. In 2005 he appeared on American current-affairs show 60 Minutes with Ed Bradley, who put the question to him. "It goes back to the destiny thing," Dylan replied. "I made a bargain with it, you know, a long time ago. And I'm holding up my end." "What was your bargain?" "To get where I am now." "And who did you made the bargain with?" "You know, with the chief commander." "On this earth?" "On this earth and in a world we can't see."

I spoke to Bradley a few months after he did the interview, and he agreed that, though Dylan smiles occasionally during this encounter, his body language is not that of a man who is joking.

Just taking a flier on this for a moment, and assuming that he has not entered into a pact with Satan, perhaps one advantage to touring is that, these days, the singer appears able to keep his distance just as well when on the road as off it.

This was not always the case. The last writer to get close to Bob Dylan on an everyday basis was Larry "Ratso" Sloman, who began by accompanying him as a journalist on the 1975 Rolling Thunder Revue tour and wound up co-producing his video for "Jokerman".

Amid the notorious debauchery of the Rolling Thunder Revue, Ratso managed the not inconsiderable feat of standing out as sleazy; he was given his nickname (inspired by Dustin Hoffman's low-life character in 1969's Midnight Cowboy) by Joan Baez. "I wouldn't do it again," Sloman told me. "I was young and I was broke."

Ratso bonded with Dylan after losing his temper in a hotel lobby in Vermont. "I don't need this humiliation and abuse," he complained. "I can write about other things. I'm going home." "What is it that you need, Ratso?" Dylan asked. "Be specific." "I need access." "You need Ex-Lax?"

There is one thing that never deserted him, I suggest to singer Kinky Friedman, who briefly travelled with the Rolling Thunder Revue, and that is his sense of humour.

Friedman recalls taking a flight when there were no first-class seats left. "There were only a few seats left in coach and Bob found himself seated next to a young female fan. 'I can't believe I'm sitting next to Bob Dylan!' she screamed.

'Pinch yourself,' said Bob."

There are, according to one well-placed source, widespread misunderstandings about the way Bob Dylan works and lives. First is the notion that he lives permanently on the road. This springs from the title of his Never Ending Tour, a phrase originally invented by a journalist. "On average," a colleague said, "he spends around a hundred nights on the road." This is by no means unique or - in an age where profit is increasingly driven by ticket sales - even exceptional. "The other thing that might surprise people is that his life when he's travelling is remarkably normal. He stays in relatively modest hotels. When he goes out, though he has security, he isn't accompanied by dozens of bodyguards." "Observation of people and places," one musician told me, "has always been very important to him - whether that means wandering around New York at night, or visiting a new town. Bob Dylan is extremely curious. The great thing about being on the road is that it allows him to be anonymous without being isolated. And he really likes to be anonymous."

This view would seem to be confirmed by a few recent incidents involving the singer. "What kind of alchemy," Dylan asks, in Chronicles, "could create a perfume that would make a reaction to a person lukewarm, indifferent and apathetic?" If such a scent could be made, he adds, he'd like some.

It seems that the singer must have got his hands on a bottle and applied it with gusto one day in July 2009, when he took a stroll away from his tour buses, which were parked outside a hotel in Long Branch, New Jersey. When he wandered into the garden of a property displaying a For Sale sign, the occupants called 911 complaining that an "eccentric-looking old man" was on their land, his hood raised against the heavy rain. "I asked him what his name was," said Officer Kristie Buble, 24, "and he said, 'Bob Dylan.' Now I'd seen a couple of photographs of Bob Dylan from years ago, and he didn't look like Bob Dylan to me at all. He was wearing black sweatpants tucked into black rain boots, and two raincoats with the hood pulled down over his head.

So I said, 'OK, Bob, what are you doing in Long Branch?' He said he was touring with Willie Nelson and John Mellencamp."

The officer took him back to the bus, where she was shown his passport. "I wasn't sure," she explained, "if he'd come from one of the hospitals." Bob Dylan, she added, was courteous throughout.

Creativity, Dylan says in Chronicles, "has to do with experience, observation and imagination. If any one of those elements is missing, it doesn't work." The silent contemplation of other lives seems to have been an important part of his working process from the start. One of the most uncomfortable filmed interviews he ever gave - a title not easily gained - was in Toronto, with documentary director Christopher Skyes, in the star's trailer on the set of the 1987 film Hearts Of Fire. (Reg Presley of the Troggs, who appeared as a guitar-playing extra, told me he was approached on set by Dylan. "He said, 'How long have you been carrying that instrument around?' So I said, 'All bloody afternoon, mate.'")

Richard Marquand, director of Hearts Of Fire, told Sykes, who was filming an Omnibus special, that the singer was "a pussycat" and "a joy" to work with. The director died of a heart attack before the film was released.

Dylan, who is no stranger to using silence to intimidate, sketched Sykes during their brief session. This allowed the singer to be even less voluble than normal, and put the director in the unenviable position of having to supply the bulk of the conversation. "I read this article," Sykes says. "It was about Schubert." "Yeah?" says Dylan, with a mutinous glare. "The guy was saying that, listening to these Schubert songs, you had to think that he was connected to some kind of pipe, down which all this stuff came."

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A pause. "A pipe?" Dylan repeats, scenting blood. "Yeah," Sykes replies. "Some sort of a pipe, or conduit. He couldn't kinda grasp how this guy Schubert was writing these things. Where do your songs come from?" "I can't tell you that 'cause I'm not God." "I think," Sykes says, "I'm going to have to look at my list of questions." "Oh, yeah," says Dylan, who has taken it. "Here's your list."

Just as you think the session is going to grind to a humiliating end, Dylan volunteers one of the very few Zimmermanesque reflections ever captured on film. "Fame," Dylan says, "it's like... When you look through a window, say you pass a little pub, or an inn. You look through the window and you see people talking and carrying on. You," he continues, avoiding the intimacy of the first person pronoun, "can watch outside the window and see them all being very real with each other. But when you walk into the room, it's over. I," he continues, repossessed by the spirit of Dylan, "don't pay any attention to it."

On May Day, 2009, Dylan showed up at Mendips, the childhood home of Beatle John Lennon, now a museum (his visit was mentioned in Alexei Sayle's 2010 BBC Radio Four documentary, The Lennon Visitors).

He booked under a pseudonym, travelling, as any visitor is required to, on a shuttle bus that he boarded at Speke Hall. His fellow passengers were three ladies from North Wales. Since he had his hood up on the bus, he went unrecognised, until he met the previous group of visitors coming the other way down the drive. "He was genuinely interested in the house," curator Colin Hall told me. "He spent most time in rooms where songs might have been written or rehearsed." Dylan, he added, was particularly taken by the books in Lennon's bedroom: Alice In Wonderland, which he knew, and Richmal Crompton's Just William, which he didn't. "The whole experience," says Hall, a former teacher, "felt surreal. It was like meeting Shakespeare."

Speaking in the early Eighties, Bob Dylan said: "I don't think I'm going to be understood until a hundred years from now. When I'm dead, maybe people will realise that, and then figure it out."

Even now, it's certain that his reputation as an American legend in the tradition of Mark Twain and Walt Whitman is assured. But is he a poet in the traditional sense? While it's true that Allen Ginsberg or TS Eliot would be anything but ashamed of a line like "the ghost of electricity howls in the bones of her face", from "Visions Of Johanna", they would most likely not have chosen to rhyme "kelp" with "help", as he does in his captivating eulogy to his first wife, "Sara". The truth is that, however much ink has been spilt on this subject (and, for what it's worth, I write this as a former pupil of the late Stephen Wall, close collaborator of Dylan's chief academic advocate, Christopher Ricks, professor of humanities at Boston University) it doesn't matter.

Dylan is, was and always will be rock'n'roll; the key to how he can get away with a line that looks ghastly on the page is simply the mesmeric power of his voice.

But how about the widely held belief that Dylan's output experienced a hiatus for - depending on your view - two decades or more, from the late Seventies onwards? "Anyone who wants to ignore particular periods of Bob Dylan's work is entitled to what I would consider their rather ignorant opinion," Elvis Costello replied, via e-mail. "To do so would be to dismiss 'Every Grain Of Sand' and 'Ring Them Bells', two of Dylan's most beautiful songs, and numerous others, such as 'Brownsville Girl' and 'Blind Willie McTell'. Not to mention the performances that came from returning to the folk canon for World Gone Wrong [1993]. Much of the writing of power and worth since that time was predicted by that record."

With somebody of Dylan's stature, Costello goes on to suggest, it is also possible for a great song to slip past you. "If I had to cite just one claim to Bob Dylan's strength as an artist in recent years," he wrote, "it would be 'Cross The Green Mountain'," a recording made for an unheralded movie about the American Civil War called Gods And Generals, released in 2003. (The song appears on The Bootleg Series Volume 8: Tell Tale Signs.) "At seven minutes, the composition is on a scale few writers could sustain. Images mount up in a monstrous dream of war; victims are seen as decent men even as they fall. Dylan's singing is subtle and nuanced throughout: sometimes grave, other times cruel and at last shattering, when a death notice is received from the front. It is the closing line: 'We loved each other more than we dared to tell' that is most tenderly sung, and the one that catches the tragedy of a divided Union. Maybe," Costello continues, "this is why a wonderful song such as this may outlast the hall of mirrors and misapprehensions about its writer, as if a person should ever be a riddle to be solved." "Bob Dylan," somebody once said, "has so many sides that he's round." It's perhaps inevitable that, as you work through archive footage and listen to other people's recollections, his less sympathetic attributes come to the fore. As a single force in his life, envy has been as powerful as any. But in the course of researching this article, I spoke to two people who consider Bob Dylan to have saved their lives, through the help he gave them to escape narcotic addiction: one a musician dependent on heroin in the early Nineties, the other, singer Cerys Matthews. "One thing people don't realise," says actress and musician Ronee Blakley, "is that Bob is extremely vulnerable. Once we were staying in a smallish hotel in Massachusetts. Bob and I were alone in a large reception room, waiting for people to greet him. He looked at me and said, 'Ronee - help!' I said, 'Help? Help what?'

Then I realised: he was terrified of the onslaught of strangers."

The punishing nature of touring, Ronee goes on, "is rarely acknowledged. Not just the grind of travel, but the holding of the guitar; over the years, it wears down your back and your neck. He switches to piano for most of the show. You could almost say he has sacrificed himself for his art."

Punished or not, Bob shows no sign of letting up. In April there is an Australian tour, and work has begun on a follow-up to No Direction Home, this time dealing with the Rolling Thunder Revue tour. He's rumoured to be working on a movie soundtrack.

Dylan is also committed to deliver two more volumes of Chronicles and four other books. In his spare time, he constructs metal sculptures using an arc welder.

Dylan recently noted that Picasso "went on till he was 90". He has not gone on record as stating in what other artistic company he'd like his name to be remembered. But in 1985, dropping his guard in the company of the English journalist and biographer Mick Brown, this most reluctant of interviewees did consent to give a list of the people he himself would like to question for the record. "Hank Williams," Dylan said, "Apollinaire, Joseph of Arimathea, Marilyn Monroe, John F Kennedy, Mohammed and the Apostle Paul. I'd like to interview people who died leaving an unresolved mess behind. And who left people for ages, to do nothing but speculate."

Originally published in the May 2011 issue of British GQ.

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