There's no let-up for Hollywod's most controversial director – the sequel to Wall Street, a documentary about Hugo Chávez and his most ambitious and personal project to date, the secret history of America

The following correction was printed in the Observer's For the record column, Sunday 25 July 2010

The United States awards the Purple Heart to those wounded in combat; it is not a bravery medal.

Oliver Stone is a man's man. Of this I have no doubt before meeting him. Not just because of his status as a sort of latter-day Ernest Hemingway, an action man with a reputation for women and drugs who won the Purple Heart for bravery in Vietnam, and then an Oscar for reproducing his experiences on celluloid. But because the most compelling sequences from his latest film, a documentary called South of the Border, show him hanging out with Venezuela's president, Hugo Chávez, chewing the cud about politics and war, talking very much mano a mano.

It's an impression that's reinforced moments before I meet him in his Los Angeles office when the photographer appears and shows me some of the portraits he's taken. They're slightly startling because Stone has a new moustache, a big, bristling, Zapata number, and in the tiny digital frame on the back of the camera, he looks like it's him who really ought to be dressed in military fatigues and running his own small South American regime.

Then he ambles in, distractedly. "Suzie!" he calls to his co-producer. "Where are my glasses? I think I've lost my glasses."

We both look at him. He has one pair of glasses on the top of his head. And another pair on a piece of cord around his neck.

"They're on your head," says Suzie.

"Do you think you could go and look for them? They're very valuable to me."

Suzie hesitates and then, having seemingly witnessed this sort of situation before, says: "OK!" and disappears out the room. Two minutes later, Stone puts his hand to his head. "Suzie! I've found them! They were on my head!"

Suzie reappears at the door. "I know," she says. "I told you."

"Did you? Jesus! What, now I can't even hear?"

It's a rather nice surprise, this. The bumbling, the self-accusation, the absentmindedness. On paper, he's so much the alpha male that, as one interviewer put it: "One expects to find antler stubs under his thatch of suspiciously too-black hair." As well as his war record, there are his various arrests for possession of drugs, as well as his well-rehearsed views on monogamy ("unnatural"). But, mostly, there's the work.

There seems an almost hyper-masculinity to Stone's oeuvre. He's the director of Platoon, one of the most highly rated Vietnam films of all time, a film that was based on his experience. The war spawned a further two films, Born on the Fourth of July and Heaven & Earth. He made one of the most violent and controversial films of the 90s, Natural Born Killers. And he's had a fascination with some of the most powerful men on earth, having made films about no fewer than three American presidents: the Oscar-winning JFK, Nixon and, most recently, W, about George W Bush.

In the flesh, however, he's more like an amiable professor. There's a sort of otherworldly air of distraction and he reminds me of one of those old-fashioned Marxist academics who have now all but disappeared. Although he's not a Marxist, he has a strictly Stoneist view of the world and to this end he has facts, figures, theses, arguments, names, dates, an entire view not just of contemporary politics but also history.

But one of the most appealing aspects of Stone is the sheer depth and breadth of his interests and ambition. In addition to tackling socialism (and how Chávez has fanned its flames across South America) in South of the Border, he has also, this year, taken on capitalism in Wall Street: Money Never Sleeps, the much-awaited return this September of Gordon Gekko to a Wall Street where greed isn't just good, it's legal. Two films, two ideological systems, and yet this pales in the face of his next project: a 10-part documentary series for HBO, Oliver Stone's Secret History of America.

He's right in the throes of it. "It's my big project. It's something I want to leave behind. And we're now in the third fucking year of it," he says. "It's a war. They're in that room next door working on it right now. It's an ongoing odyssey."

It's a truly massive project, a personal mission, the encapsulation seemingly of all that Oliver Stone has thought and read and felt in the 63 years of his life so far, and by the end of the interview I feel slightly anxious about it on his behalf. After all, Stone's passion projects haven't always ended well. Platoon did. It was the film that he had to make, a heavily autobiographical account of his Vietnam war, "a grunt's-eye view", and won him his second Oscar (his first was for writing the screenplay of Midnight Express). But Alexander, his magnum opus, a biopic of Alexander the Great that he at one point calls "his life's work", was savaged by the critics.

The reception of South of the Border in the States is, I imagine, a small taste of what is to come. If Platoon was a grunt's-eye view of war, South of the Border is a leftie's-eye view of South America and he's spent the last few weeks fighting off criticism: that he's a patsy; a Chávista; that he didn't speak to any of the opposition figures. "But that wasn't what we set out to do!" says Stone. "I let him talk. That way you see him as he sees himself. It's a psychiatrist's technique."

It's interesting that he brings this up. He's been in analysis three times, he tells me later. But the biggest surprise about Oliver Stone, and perhaps his greatest contradiction, is that for somebody who is such a doer, who has such a relentless drive to work, who has done and accomplished so much, who started his career writing scripts for Scarface and Midnight Express and has gone on to direct nearly 20 feature films and several documentaries – is that he's also an introvert and a self-critical one at that.

He can quote, verbatim, unfavourable reviews he's received years after the event. More than this, there's an introspective aspect to his nature that is quite at odds with the macho persona. And, for all the argument and theorising, it becomes apparent that Stone is a creature of his emotions. He makes the films he does because he feels he has to. Many of his career decisions seem to be motivated not by good sense, money or the esteem of his peers – he's driven by something far more internal than that.

In an old interview, Stone once said that his films are an "emotional barometer" for him. The violence of Natural Born Killers came out of the anger and sadness he felt when his second wife and mother of his two sons, Elizabeth, left him. So, I wonder, what attracted him to the competing issues at stake in South of the Border and Wall Street: Money Never Sleeps?

"My father was a Republican. And he hated Roosevelt. And that's sort of been the battle of my life, I think. You have to understand that I grew up a Republican conservative. I hated Castro. And I put my money where my mouth was because I went to war, but I understood pretty quickly that this was another place, another culture, and we would never fit in there.

"It's the same story in Afghanistan, Iraq and South America. It's white people meeting people who they think they are better than. And I feel that this war is the war of my life. I've seen it over and over again and if I can do one thing with what's left of my remaining years, it's just to cry it out and say it, I hope, with enough entertainment that people will want see it."

In this context, South of the Border is simply another variant on this, his life's work. What the film makes clear is how much of a bogeyman Chávez is in the United States. The first half of the film, a not-altogether-successful Michael Moore-esque homily, features clips from the US news media (or "the missile shield", as Stone refers to it) with Fox News declaring that Chávez is "as big a threat as Osama bin Laden".

It's in the second half that the film comes to life, though, where Stone meets Chávez. "I liked him. He's very warm and very gracious. And he's a bear. I've always said that if he looked like Woody Allen he'd play a lot better with the world press. I think men are threatened by his physicality."

The affection seems to be mutual. At one point, standing on a runway in the dark, Chávez points to a building where he was imprisoned during a coup and where some of his men lost their lives. "As an ex-soldier I understand," says Stone and Chávez rests his hand upon his shoulder.

Making a documentary "was the last thing I wanted to do," says Stone. "It was Fernando Sulichin who I worked with on Comandante [the 2003 documentary of Stone interviewing Fidel Castro] and who is funding Secret History who suckered me in. And we went and we talked to Chávez and he said, 'Don't just take my word for it; go and talk to these other presidents.' So that's what we did, we went on this road trip." He jaunts off and chews coca and talks socialism with Bolivia's Evo Morales and meets Brazil's Lula da Silva, Paraguay's Fernando Lugo, Ecuador's Rafael Correa and Cuba's Raúl Castro. "The result," says Stone, "is this weird little thing. What is it? It's not a documentary."

It is, just not an entirely sane one, with two halves that don't quite fit together, but it's still a fascinating glimpse of Chávez and an overview of a massive popular movement on one of the largest continents of the world.

"I'm not an interviewer, I'm a director. And I go to these places and take advantage of the status that I have as a film-maker and can treat the person like an equal. And I'm not hostile. I give them face time. We don't even know the names of these guys in the United States."

Fundamentally, Oliver Stone is doing it his way because he can and because he's spent his life doing things his way. He's as idiosyncratic as they come, jumping from genre to genre, from indie documentaries to studio blockbusters. Hitting spectacularly with some (he's won three Oscars), missing spectacularly with others (Nixon, like Alexander, was brutally panned). He's always been impossible to pigeonhole, to predict quite where he'll go next.

There are high hopes for Wall Street: Money Never Sleeps. I rewatch Wall Street on the plane over and enjoy it as much as I did when I first saw it years ago. It's completely of its time – mobile phones the size of breeze blocks, an array of kitchen equipment so dazzling it gets its own special sequence (I give you the microwave and the hand-held blender). But it has stood the test of time.

Released in 1987, it was a brilliant, prescient taste of what was to come: the crash later that year; the insider trading scandals. I also spot Stone in a cameo I hadn't noticed before. He's plays a moneyman, a financier.

"I was playing my father, Lou," he says. And, had the 60s and Vietnam not blown him off course, it's what Stone might very well have become. It was what he was born to. His father was a stockbroker, who met Oliver's French mother in Paris during the second world war. Stone had a privileged, if emotionally austere, upbringing at an east coast boarding school. His mother was often absent and then disappeared altogether: aged 15, his headmaster called him into his office and informed him that his parents were getting divorced.

He went to Yale – he was in the same year as George Bush – and it's here that his conventional, bourgeois upbringing breaks down. He dropped out, deciding first to try to write a novel and then to enlist.

I read a quote, I say, where he says that he felt he wouldn't be properly human if he didn't know what war was. "There was something bugging me," he says. "Yale was a problem for me. I was not a happy young man. I didn't feel good in my skin. I'm glad I left but it was very painful at the time. My father thought I was pissing away my life. I was becoming an infantry soldier and I was going to become one of life's unfortunates. I wasn't going to amount to much. He was worried. And frankly so was I."

You've spent the rest of your life proving him wrong? "In a way, although it took me years. Coming back from Vietnam was extremely difficult. My father did, towards the end of his life, believe that Vietnam was a mistake, but we had many, many fights about it."

What would your father have made of the Wall Street of the last few years? I ask. "Look, he was pissed off when we left the gold standard in '73, although'73 is actually very interesting. It's a really crucial year, because the income of the average working man flattened out in '73 and never went up in spending ability. But meanwhile the productivity of America went up like this. Where did that money go? It went to CEOs and stock holders. It went to the banks."

The most remarkable aspect of Wall Street was that the villain of the piece, Gordon Gekko, became a hero to a new generation of moneymen. Michael Douglas claims that he's unable to go out for dinner in New York without having a hedge fund manager slap him on the back and thank him for inspiring him to enter Wall Street.

But if the first film was an old-fashioned, rite-of-passage story about a young man, Bud Fox, corrupted by greed, is there a take-home message from Wall Street 2?

"It's a fun movie, an entertaining movie. The first one I think you'd say is a morality tale and I think this one is too. In the sense of what is important? Are there more important values than money?"

Were you wary of glamourising it, given what happened to Gekko?

"It's 23 years on and greed will go on for the rest of times. And envy. Envy plays a big role in this film too. If you pass all the regulations in the world, they'll try and get around that. I have no problem with people wanting to make money. But don't make the banks into hedge funds, which is what they did.

"There's something Douglas says in the movie. He says that in 2008, of the corporate profits in the US, 47% were from finance-related companies. In the old America, it was 17%. It became the main business of America. We became a giant casino."

There is a father and son at the heart of the first Wall Street, as there is in much of Stone's work. It's a relationship that has clearly preoccupied him. But Lou Stone was perhaps not your standard, uptight New York stockbroker: he paid for Stone to lose his virginity to a prostitute at the age of 16. Stone has raised two sons himself now – Sean, 26, and Michael, 18. Has that made him see his father differently?

"Sure, but even before I had my sons, I was very father-oriented. He was a very powerful man. But you must remember my mother was very powerful too."

Ah yes, his mother. Jacqueline Goddet met Lou Stone when he was working as an aide to Eisenhower. She does sound like an extraordinary character, I say. "She still is – she's 88 and a party animal. She loves people and they love her. She called me the other night and she'd been out on the 4th of July weekend until two in the morning."

Perhaps Stone's greatest exploration of his relationship with his mother is in his novel, A Child's Night Dream. He started writing it when he was 17 and returned to it at 50, a period that he refers to as his midlife crisis. "I'd been criticised and loved, and criticised and loved, I mean, really, extremely… Nixon had just come out and had flopped. And I loved Nixon. I thought it was one of my more mature works and it had not been well-received. But it didn't matter. I returned to the book. I knew that it would never have a big circulation, but it mattered to me and I got it out. I just stopped making films for two years and basically did that. I think I lost my way and I felt like the book was putting me back."

Was writing the novel a way of reckoning with the past and in particular his mother? After all, there is a character called Oliver Stone who is sexually obsessed with his mother… "Yeah, well, there were two Stones, William and Oliver; they were two sides to me. But, yes that's correct. There was no incest, but my mother was very French and very free. It wasn't a big deal to walk around naked in the house and stuff like that."

I tell him about an extraordinary quote I have found from her a few years ago, where his mother says" "Oliver didn't just love me. He was in love with me."

"Is that right?" he says. "Ha, ha, ha. Well, she was a great tease. If that's the case, it's a classic Freudian case, the frustrations of an Oedipus complex. The son wants the mother but never gets her because she's the first woman in his life."

"Does that make sense to you?" I ask. "The Freudian explanation?"

"Absolutely. Your mother's body is the first thing you know and, frankly, it's very attractive and it turns you on. But you don't know what to do so it's a tremendous puzzle."

Usually, when an interviewer discovers something interesting about a subject, it's repeated in every article thereafter, but I find only one piece from the mid-90s, an interview with Elizabeth Stone, in which she claims that it was his mother who initiated him sexually. She says that Jacqueline had told her: "He couldn't relax and I had to show him."

"It's not clear," the interviewer goes on, "from detailed interviews with Elizabeth, Oliver and his mother, Jacqueline, what actually occurred. Elizabeth claims that Jacqueline Stone touched her teenage son's genitals and masturbated him. Jacqueline heatedly denies it."

So, I ask him straight out: "Did your mother teach you how to masturbate?"

"Well, I can't live with denial – sure."

"She physically showed you?"

"It was no big deal. It's not English. It's French. It was no big deal. I wasn't attracted to her. You have to understand. After a certain point, I grew up and I moved on. And I've had successful relations – with everybody!"

He says this a joke, but it's also true. He is a self-confessed womaniser. Elizabeth, his second wife, (his first, Najwa Sarkis, was Lebanese ) is said to have left him after having finally run out of patience with his extramarital dalliances. "It's on the record," says Stone. "And I don't like to lie. That's bullshit. It's not a big deal… I'm not running for office."

The Asian mentality is very different, he says, to the Anglo-Saxon one. "That's why I loved Asia when I was young. When I went over there, it was a revelation. I could never quite come back. I always had difficulties readjusting to the Anglo-Saxon mentality with women."

It is why his third wife, Sun-jung Jung, understands him, he says. "She's cool. She's Korean. Different mentality. Mutual respect… she laughs and trills and she sings when she speaks. I love the sound of her voice."

Their daughter, Tara, is 14. "She's part of that new generation, Asian-American. We're really going through it now. I mean, she's 14 – she does respect me but she does give me a hard time. But it's fun. She's smart. We go to the movies. She loves talking about movies."

Has having a daughter changed his attitude to women? "Yes it has. It's harder to be blind. Sometimes, you have to be blind to jump into some of these things, but when you see your daughter in some of these women… you see the human side more clearly than before."

I wonder aloud whether his relationship with his daughter will inform his female characters. His films have always seemed to me to be explorations of masculinity, of male relationships, in one form or another, but then his world, for years, was male. He was an only child and incarcerated for years in an all-male boarding school, before going to an all-male Yale. Discovering women in Vietnam, he says, he felt like Gauguin in the South Seas. "They were these ripe fruits."

He starts reciting his female characters, finishing with Olympias, Alexander's mother. It is abundantly clear from everything he says that Alexander was the project of his life. "It was. That's why I went back three years later and did a third version of it. If you could ever see it – it's the right version of it. The editing was rushed… I was never able to… frankly it's a complicated vision and I'm fighting to get it recirculated. In England, there is a release of it, but it's very little known because it was so slagged at the time. It was very painful to me."

Of all the films, it's his most autobiographical, he says. That's a strange statement given that its subject concerns the greatest emperor who ever lived, but then he is also the vulnerable son of all-powerful parents. He first dreamt of making it as a film student, he says, and it was during that midlife period of reflection that he came back to it again.

"I remember feeling like I had lost my way. The book was important and so was Alexander. I do think that there is the idea what you are when you're young, you must stay faithful to something in there."

This is one of his core beliefs. His teenage years are still the crucible of Oliver Stoneness on which he draws. They were so extreme, in almost every way. From the emotional barrenness of boarding school ("For years, I thought it was a disaster; it had taken the love out of my life; there was no sense of humanity"), those odd experience with his parents and sexuality, through the privilege of Yale and finally, apocalyptically, Vietnam. You really don't need to be a Freudian to read something into this. His ex-wife, Elizabeth, has put it more bluntly: "That little boy didn't stand any chance of any normal sort of life."

He's an assiduous diary-keeper and regularly rereads ancient entries to check up on himself. In 2000, he even decided to relive the acid trips of his youth. Under the supervision of three psychoanalysts, he sat on a mat, put an eyemask on and took LSD. It lasted nine hours and was, he says, because he wanted to relive past experiences with the drug "under more scientific conditions".

He's gone through various stages of taking drugs, mostly psychedelic ones. "Heavy trips," he calls them – in Oliver Stone there's a small part of the 60s that never died. He tells me about being "frightened to death" on one of them. So why did he do it? "Because of the adventure."

Ah yes. The adventure. That other Oliver Stone hallmark. His cousin James says that Stone went to war because: "Anything he could do to be at the edge, and to experience more than other people had experienced, and to shock, he was likely to do. It was consistent for him to want to experience the most intense thing that was going on then in the world."

Even now, there seems to be no letting up. The hell-raising days may be over – although I wouldn't bank on it – but there still seems to be this lust for experience, as evidenced by South of the Border. At an age where most men might start thinking about golf, Stone is chasing socialists across South America.

He's as committed as he ever has been, if not more so. Politically, workaholically. There's still a relentless drive to work, work, work. It's coming up to 9pm by the time I leave his office and nobody seems to be making a move to go home. His film editor has been waiting patiently for him in the room next door, ready to attack yet another section of Oliver Stone's Secret History of America. There's another documentary on Castro to come – the third part of his trilogy. He'd like to do an update to his novel, he says, some sort of epilogue. There are the final edits on Wall Street: Money Never Sleeps. And then there's South of the Border to launch in London. And defend from attacks all over again.

I fear for Oliver Stone's Secret History of America. Oliver Stone will do it Oliver Stone's way, whatever the critics think. He exhibits an artist's singlemindedness, an ideologue's obduracy. If his ambition occasionally exceeds his talent, it's not because his talent is small, but that his ambition is so very, very large. The Alexander comparison is really not as far-fetched as it might seem: he really is trying to remould the world according to his vision. Watch out, world.

• This article was amended on 21 July 2010. The original referred to Suzie as Oliver Stone's assistant. This has been corrected.