"This social phenomenon – in no way was it ever in existence in the past and in no way will it ever exist again," the American rock promoter Bill Graham told filmmaker Tony Palmer in 1975. "I don't think we'll ever see this again – the adulation, the massness."

He was talking about the phenomenon of Led Zeppelin, then the biggest band in the world. Coming from a man who, two years later, would suffer a notorious run-in with Led Zeppelin in Oakland, California, these were prescient words. For rock music never has surpassed the "massness" Zeppelin then enjoyed, a story told in my new oral history of the group, Trampled Under Foot.

"The legions of disenfranchised young American warriors had no outlet whatsoever," says the singer Michael Des Barres, whom Zeppelin signed to their Swan Song label. "Led Zeppelin came along and gave them a hard-on like they'd never had before. Their lives became three chords and a stadium parking lot. There was no TMZ, no internet. There was just this incantation, this wailing to the gods."

At a time when rock consists of little more than footnotes to the Big Bang that began with Presley and burned out with Cobain, it's hard to explain the scale of Led Zeppelin's 70s success except by framing it in terms of a kind of cult worship. Their final British gigs – two shows at Knebworth in 1979 – were watched by an estimated 200,000 people. But it was in the US where the cult of Zeppelin was at its deepest.

"America fell in love with Led Zeppelin because most people hadn't had the opportunity to see the Beatles," says Denny Somach, producer of Get the Led Out, a long-running Zeppelin segment that is syndicated on classic-rock radio across the States. "Zeppelin became a religion."

"They redefined the 60s in the image of all teenagers for whom hippiedom was a cultural given rather than a historical inevitability," wrote Robert Christgau of the Village Voice. "All the kids forced by economic reality and personal limitation … to settle for representation of power because the real power their older siblings pretended to was so obviously a hallucination."

The music had something to do with their success, of course. After suffering critical scorn for much of their existence and then being forgotten for most of the 80s, only now are Zeppelin being embraced by pop snobs as the eclectic and mercurial unit they were. Guitarist Jimmy Page, bassist/keyboard player John Paul Jones and drummer John Bonham were three of rock's most united, thrilling players, and Robert Plant the most frighteningly exciting hard rock singer who ever shrieked into a microphone.

The critics didn't know, but the young boys understood. "Zeppelin had this exotic otherworldly appeal," says Brad Tolinski, author of a forthcoming collection of interviews with Page. "They took us out of our environment. But unlike prog rock, it had real balls to it."

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Led Zeppelin's first six albums – from Led Zeppelin to Physical Graffiti – remain by some distance the greatest hard rock records ever made. They're great soft rock records, too, for that matter, the unplugged Friends and Going to California easily the equal of sledge-hammering classics like Whole Lotta Love and Immigrant Song.

But the astounding music wasn't the whole story: it never is. The psychic investment in Zeppelin as "your overlords" (to quote Immigrant Song) reflected rock's evolution from the boys-next-door Beatles to the orgiastic longhair communion of festivals like Woodstock.

"Led Zeppelin were both dangerous and spiritual," notes LA svengali-scenester Kim Fowley, a pal of the band's in their heyday. "They get you with all that maudlin melancholy acoustic music from Wales, but then they have the Willie-Dixon-derived blues stuff going on at the same time. The mystery kept people coming to the live shows, and they got to read meanings into the lyrics that weren't there."

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The mystery lies in the association of Zeppelin with the occult, and the appeal to adolescents of that hint of darkness cannot be underplayed. Millions were convinced they heard satanic messages recorded backwards on the epic Stairway to Heaven. Jimmy Page's fascination with the writings of Aleister Crowley – he even bought Crowley's old mansion – proved irresistible to kids searching for dark magic in their anonymous suburban lives. His beguiling ZoSo symbol, seen on the sleeve of the band's huge-selling fourth album in 1971, became an iconic magnet for a generation.

"The children of ZoSo are Zep's legacy," wrote Donna Gaines, a sociologist and music writer. "Mostly white males, non-affluent American kids mixing up the old-school proletariat values of their parents, mass culture, pagan yearnings and 60s hedonism."

Stoking the mystery was the group's larger-than-life manager Peter Grant, who – knowing that word-of-mouth was the most potent marketing tool of all – consistently refused to release singles or allow the band to perform on television. "[Peter] defended the band as though they were his only children in life," recalled the late Ahmet Ertegun, founder of Atlantic Records, the label that signed Zeppelin in 1968. "He was a sensational manager – he built an aura of mystique around that group that still exists."

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Only in 1973 did Zeppelin decide to emerge from behind their PR shield and allow fans a peek behind the scenes. Even then they chose not to ape the social aspirations of their great rivals the Rolling Stones. Where Mick Jagger wanted Princess Lee Radziwill in his dressing room, Zeppelin's idea of glamour was the sixth floor of the Continental Hyatt (or "Riot") House on LA's Sunset Strip. Here they held court, mad dogs in the California sun attended by a retinue of drug dealers and underage groupies.

"I'd be on the road writing for the NME, and we'd check into the Hyatt and Zeppelin would be there," recalls Mick Farren. "The whole place was full of the stinkiest fucking groupies. Keith Moon actually blew up hotel rooms, but with Zeppelin it just seemed to be running in semen and beer and unpleasantness."

Los Angeles was where things began to unravel for Zeppelin and their heavy friends. The sheer depravity of their behaviour in the city – dangling people over balconies and chaining groupies to radiators – topped anything British bands had previously perpetrated in America. "Something about Zeppelin's energy really altered the joie de vivre of the LA rock scene," says super-groupie Pamela Des Barres. "They thought they could get away with anything – and they could."

So where do you go from the top of the entertainment mountain? That's right, downhill – creatively, physically and morally. After 1975's Physical Graffiti, they were never the same creative force. Page sank into heroin addiction, Bonham into the chronic alcoholism that killed him – and thereby ended the group – in 1980.

The group's last show on US soil followed the incident in Oakland. First a security guard, Jim Matzorkis, was attacked by John Bonham after a perceived slight against Grant's son, then Grant – aided by John Bindon, a psychopathic actor and semi-gangster recruited to the entourage – followed up, more brutally. The incident was hushed up, and Zeppelin left the city after charges were brought against four people, including Bonham and Grant.

A day later, Robert Plant's five-year-old son Karac died from a respiratory infection, a devastating loss that almost made the singer walk away from music forever.

As a narrative, Led Zeppelin's is an old fable: be careful what you wish for, and never fly too close to the sun. Plant survived to tell his tale and to blossom as a solo explorer. Jones always took the mega-success with a pinch of salt anyway. Only Page seems stuck in his past, surviving on a steady diet of awards shows and Classic Rock magazine covers.

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Could the surviving trio ever reunite for a swan-song tour, capitalising on the great show they staged at London's O2 five years ago in memory of Ahmet Ertegun? Probably not.

"It would be so interesting to have a candid conversation with the three of them sitting there and know that they were over it all," says Benji LeFevre, Plant's vocal engineer from 1972 to 1985. "Clearly they aren't."

Still, it would take a fool to completely rule out a hugely lucrative reunion. "Robert wanted to prove his success on his own and he did," says Lori Mattix, Page's favoured groupie in the mid-70s. "Now that's out of the way he might just go there, because he'd like that adoration one more time."

"My guess is that sometime in the next five years, Robert will call Jimmy and John Paul and they'll do a tour," says Danny Goldberg, the former US president of Swan Song. "It's still an extraordinary opportunity."

• Barney Hoskyns's oral history Trampled Under Foot: The Power & Excess of Led Zeppelin is published by Faber & Faber on 6 September. A special Led Zeppelin night featuring Barney Hoskyns and special guests takes place on Thursday 13 September at 7pm at Rough Trade East, Old Truman Brewery, 91 Brick Lane, London E1 6QL