Will Smith as Ali with Nona Gaye - Marvin’s daughter - as his wife Belinda

More importantly, the actor had to learn how to move like a man who - floating like a butterfly, stinging like a bee - changed the face of boxing with his speed and grace. Smith worked with Dr James Puffer, who runs the Division of Sports Medicine at UCLA and used to be head physician to the US Olympic team. Puffer singled out the 11 most distinctive Ali moves - the feints and shoulder movements which had helped him in his comeback in Zaire against George Foreman. In addition to practising these until they became second nature, Smith worked out, five days a week, six hours a day. When he started, he could bench-press 175 pounds. By the time he finished, he was lifting 365.

“Beyond looking like a fighter, my goal was to learn to think like a fighter,” says Smith. “To do that I had to eat like a fighter, sleep like a fighter, assess situations in life like a fighter… become a fighter.”

Mario van Peebles as Malcolm X

The results were more than impressive. “People will be very happy with what they’re going to see,” says Angelo Dundee, another of those legendary names, who was Ali’s trainer through the championship years and who worked as a technical advisor to the production. “Will’s doing a heck of a job. I had a ball watching this guy because he makes steps that Muhammad made. When he skips rope, you’re looking at Muhammad.” “He’s a comedian, he’s athletic, and he’s a hell of an actor,” adds Bingham.

But Michael Mann’s film isn’t simply a docudrama about the world’s greatest heavyweight. Equipped with the tagline ‘Forget what you think you know’, it is, in typical Mann style, an epic drama about an individual at a turning point in history. Which is not to say that Ali wasn’t a great boxer - simply that he was more than just a great boxer. Between the time when Cassius Clay won his first professional fight on October 29, 1960, to when he won back his heavyweight crown by defeating George Foreman in 1964, the United States had changed dramatically.

Such a turning point was bound to fascinate the director. But, as in all Mann’s movies, if there hadn’t been a story to tell, there wouldn’t have been a film to make. “I had to find a story I wanted to tell,” says Mann. “It begins in 1964 and ends in 1974. On one level, the story is simple: a man wins the heavyweight championship; his title is unfairly taken from him. He struggles to overturn his conviction, and he begins a quest to regain his crown. However, he discovers that time has taken its toll and robbed him of his prowess as he’s about to contest a younger, stronger George Foreman.”

Somewhere along the way, Cassius Clay became Muhammad Ali, becoming a follower of Black Muslim leader Elijah Muhammad, and refusing to fight in Vietnam with the immortal words “I ain’t got no quarrel with the Viet Cong”. He was indicted, sentenced to five years’ imprisonment and a $10,000 fine and, as a convicted felon, barred from boxing professionally in the US. It took from May 8, 1967, until June 28, 1971, for his conviction to be overturned by the US Supreme Court.

Jamie Foxx as Drew ‘Bundini’ Brown, Jon Voight as Howard Cosell and Mykelti Williamson as Don King.