Ceaselessly experimental, Altman introduced a strong element of improvisation in his work, encouraging his actors to create their characters from a bare outline and even to write their own dialogue. His experimentation extended to an unusual use of colour, while other trademarks were the zoom shot, overlapping conversations and inserting real people into his fictions.

His subjects ranged from the multi-character, kaleidoscopic Nashville and Short Cuts to intimate psychological dramas and idiosyncractic reworkings of popular genres such as the western and the thriller. Although his output was maddeningly uneven, and sometimes bordered on the pretentious, he was one of the most original and influential directors of his era.

The son of an insurance broker, Robert Bernard Altman was born in Kansas City in 1925. He was brought up in the city and was educated at Jesuit schools. During the Second World War he served as a bomber pilot, and once demobilised he studied engineering at the University of Missouri and sold a couple of film scripts to Hollywood studios. But that success proved to be a false start to his movie career, and for eight years he had to content himself with making industrial films.

This at least gave him a command of cinema techniques and eventually he decided to try again for Hollywood.

In 1957 he directed The Delinquents, a low-budget feature, and The James Dean Story, a documentary portrait of the short-lived star. Neither had much impact, and Altman decided to try television, starting with a couple of half-hour mysteries for Alfred Hitchcock and going on to write, direct and produce several hundred shows.

He eventually returned to the cinema with Countdown (1967), a story about a flight to the moon, and That Cold Day in the Park (1969), a psychological thriller made in Canada. On the strength of this modest record Altman was hired to direct M*A*S*H (1970). He was by no means the producer’s first choice, but he was suddenly a fashionable name.

M*A*S*H — the letters stood for mobile army surgical hospital — was set in Korea during the war of the early 1950s and featured two irreverent surgeons, brilliantly played by Donald Sutherland and Elliott Gould. The film was released at the height of the anti- Vietnam protests, and its black humour struck a popular chord, while critical acclaim included the top prize at the Cannes Festival.

It also spawned a long- running television series in which Altman, typically, had no part. He wanted to move on, and the success of M*A*S*H enabled him to develop projects through his own production company.

His next two films were an allegorical fantasy, Brewster McCloud (1970), and a sombre western. McCabe & Mrs Miller (1971). Then, from his own original script, he directed Images (1972), an enigmatic study of a woman’s obsession with her past lovers, which won Susannah York the best actress prize at Cannes.

Altman demonstrated his ability to breathe new life into traditional Hollywood subjects with The Long Goodbye (1973), a Seventies version of Raymond Chandler’s novel with Elliott Gould as the private eye, Philip Marlowe, and Thieves Like Us (1974), a story of two young criminals on the run previously filmed by Nicholas Ray as They Live by Night. Gould was also the star, with George Segal, of the gambling comedy, California Split (1974).

With Nashville (1975) Altman had his biggest popular success after M*A*S*H. A witty and often biting pastiche of life in the country-music capital, it deftly juggled a plethora of plots and more than 20 characters. Most of the songs were written by the actors and actresses who performed them. Altman used the same format for A Wedding (1978), which had 42 characters, and to less effect, in HealtH (1980), which charted the progress of a health food convention.

3 Women (1977) was, by contrast, an intimate study of personality change with a fine performance by Shelley Duvall, an actress whom Altman had discovered. She wrote much of her dialogue. During the 1970s Altman was not only making his own films but also producing the work of other directors such as Alan Rudolph (Welcome to LA, 1976) and Robert Benton (The Late Show, 1977).

But the critical failure of HealtH and of Quintet (1979), a futuristic fantasy about a game of death, and an unhappy return to mainstream film-making with Popeye (1980), persuaded him to take a sabbatical from the cinema. He worked in the theatre and in television on Tanner ’88, a lively tilt at American politics that included cameos from real politicians. His films of the 1980s were mostly records of his stage productions, including Come Back to the Five and Dime Jimmy Dean, Jimmy Dean (1982) and Secret Honor (1984), a one-man play about Richard Nixon.

His return to cinema proper started quietly with Vincent & Theo (1990), an intelligent, low-key biography of Van Gogh, and continued triumphantly with The Player (1992), a dark, exuberant satire on Hollywood in which more than 60 stars played themselves. It was Altman’s biggest critical and popular success since Nashville.

Short Cuts (1993), inspired by the stories of Raymond Carver, was no less impressive, a film on the epic, Nashville scale which interwove a mass of plots and characters to present an acid portrait of American society. But the Altman revival was uneven. Prêt-à-Porter (1994) was a feeble look at the fashion industry, and later films, such as Kansas City (1996), a partly autobiographical portrait of his home town, and The Gingerbread Man (1998), from John Grisham’s thriller, attracted little favour. However, he rebounded with Gosford Park (2001), a witty, lavish and well-received evocation of a grand country house party in the Thirties, with a glittering cast that included Maggie Smith, Michael Gambon, Charles Dance, Kristin Scott Thomas and Helen Mirren.

After Company (2003), a behind-the-scenes account of life in a ballet company, Altman’s last film, released this summer, was A Prairie Home Companion, based on Garrison Keillor’s radio series of the same name. Although nominated five times for a best director Oscar, Altman did not win one until this year when he was given an honorary lifetime award. During his acceptance speech he revealed that he had had a heart transplant a decade earlier.

Altman’s third marriage, to Kathryn Reed, produced two sons. He had two sons and a daughter from previous marriages.

Robert Altman, film director, was born on February 20, 1925. He died on November 20, 2006, aged 81.