When Robert Altman died on November 20th, 2006, the obituaries were almost unanimous in remembering him as a cantankerous, wayward maverick, the suggestion being that his movies were mostly haphazard, uneven curiosities, punctuated by occasional explosions of brilliance. Without question, he was a colourful, shit-kicking, dope-smoking, two-fisted drinker (retired). But to conclude that the intricate chaos and seemingly random turmoil he uniquely captures in his movies is the result of anything but a massive vision, a sophisticated grasp of structure, and a high moral sense, would be a serious mistake. He was the genius of American cinema who was never let preside.

Altman’s approach and method, his spirit and presence, were anathema to the arch-conservative studio heads in Hollywood. His first (and biggest) hit movie, M*A*S*H (1970), only got made because the Fox executives were looking the other way, believing it to be a cheap movie that would “just play in drive-ins”. Though set in the Korean War, all the political attitudes of the film were about Nixon and Vietnam. The TV spin-off (whose intentions were the opposite of the movie’s and in which Altman had no hand or part and which he regarded as obscene, given the US’s continued involvement in Vietnam) was an early example of the industry’s exploitation of Altman’s originality. His live-action version of the cartoon Popeye , regarded as weird in 1980, was followed by a wave of imitations, including The Flintstones (1994) and Scooby-Doo (2002). His enthusiastic shattering of the conventions of camera movement - the use of slow zoom, two camera set-ups, cutting from moving shots to static shots - were eventually adopted by lesser practitioners.

During the shooting of Prêt-à-Porter in 1994, I stood beside him in the huge hotel lobby where he was about to attempt to convert the real-life mayhem of a team of headstrong actors into the controlled chaos that would introduce, one by one, each of the characters who would appear in the movie. He turned to me and said glumly: “Who do I have to f**k to get off this movie?” But within half an hour, he had it choreographed - a typically exhilarating signature shot. And if anyone thinks there was anything aimless or unplanned about it, they know nothing about shooting a movie. It was sheer dogged artistry.

Altman was frequently misunderstood, despite going to lengths to explain himself with an impressive patrician authority. I saw him give a serious dressing-down to a Democratic congressman in Orso’s restaurant in New York for failing to deliver on election promises, and also the glazed expression on the face of an MGM executive as Bob pointed out to him that “All you care about is the money. All I care about is the movies.”

The combination of continual experimentation, determined criticism of the US and his interest in ideas rather than plot made him a provocative figure to the movie establishment. Elliott Gould and Donald Sutherland tried to have him fired from M*A*S*H , fearing for their careers, as what they thought was their star vehicle was transformed into an anarchic ensemble piece. The big man was deeply wounded. And, of course, ultimately the movie provided Gould and Sutherland with enough street-cred for several careers.

In Brewster McCloud (1970), he parodied the car chase from Bullitt (1968), which he regarded as irresponsible because the audience weren’t required to care about any of the people who died as a result of Steve McQueen’s driving. John Wayne described Altman’s radically different Western, McCabe & Mrs Miller (1971), as “corrupt”. But then Wayne also thought High Noon (1952) was a communist plot. Nice one, Duke. And Burt Lancaster said: “Altman isn’t a director - he didn’t give me any directions.” But that was not the way he worked. He created an atmosphere where actors could expand. On Prêt-à-Porter I proposed tentatively that I might change a line. He said: “Say whatever you like.” On another occasion he said to me: “On your entrance, I need you to stand here. Then to move here. After that, it’s entirely up to you. We’ll follow you.”

Kansas City (1996), a great film, was largely ignored. It is critical of the US, its corrupt voting system and violence, which he depicted casually rather than sensationally. That was enough to have it dismissed. But the movie, set in the 1930s, is a homage to a great era in American music. And the central relationship between the two women exposes the popular hit, Thelma and Louise (1991), as sentimental escapism.

All Altman’s movies have some element of innovation. I love the continuous druggy soliloquy of Elliott Gould’s Philip Marlowe in The Long Goodbye (1973), replacing the routine Chandleresque voiceover. But out of an astonishing extensive canon of work, I imagine most people will look to Nashville (1975), a transforming moment in American cinema, and Short Cuts (1993) - sublime achievements in a huge career.

“Nashville,” he said, “was like trying to paint a mural where the horses kept moving.”

It is a political film with a panoramic view of America, using country and western music as a metaphor. Pauline Kael described it as “the funniest epic vision of America ever to reach the screen”.

Short Cuts is an inspired adaptation of eight Raymond Carver short stories in a kaleidoscopic tragic-comic view of Los Angeles. Aficionados of Carver disputed its fidelity, but somehow that misses the point. It is pure Altman - the use of the camera, the superb editing, the command of an epic narrative and unexpectedly brilliant performances.

Most people don’t look on Prêt-à- Porter , Altman’s take on the fashion industry, as a shining example of his work. But I don’t care. It is the only time I worked with him and I loved every minute of it. I was in Paris with him and his fabulous wife, Kathryn, and you’d learn more in a day and a half with Altman than you would in a lifetime with almost anyone else. There’s a scene near the end of the movie where all these nude models parade on the catwalk. As we were about to shoot, Bob said: “Well, after all, clothes are about nakedness.” Maybe it wasn’t a huge informing idea, as informing ideas go, but I’m certain that his belief in some idea was what lifted his films onto a different level. That and the fact that he wanted to see it expressed through a whole society, not just through the angst of one central existential hero. And that he didn’t believe there were any rules about how to achieve that.

I visited him in New York in April 2006. He’d just finished A Prairie Home Companion and he was quite ill. But he was planning another movie for the fall. “Another movie?” I said. “Oh yes,” he said. “Keep goin’. Gotta keep goin’.”