Joaquin Phoenix was a surprise choice to play legendary musician Johnny Cash - mainly because he's not much of a singer. He talks to Steve Pratt about how he was moved by the film that, tragically, Cash didn't live to see.

ACTOR Joaquin Phoenix had a surprising insight into music legend Johnny Cash several years before playing him on screen. He was amazed to discover that the singer known as the Man In Black was a big fan of Ridley Scott's film Gladiator in which Phoenix was Oscar-nominated for his performance as evil emperor Commodus.

He found himself at the dinner table with Cash through mutual friend James Gray, who directed him in the film The Yards.

"He was shooting footage of John and June Carter in the studio and I think John was talking about Gladiator and Jim Gray said he knew me. John said he'd love to meet me and invited me to dinner," recalls the actor.

"He just came out with it. I was leaving and he stopped me and said he liked Gladiator. He said what his favourite part was, and then quoted this dialogue, the most sadistic dialogue I've ever heard, and relished it. We laughed about it.

"It was so fascinating to me, even before I'd started researching, that he's just gone from singing this spiritual with June, looking into her eyes and everyone was crying because it was so beautiful. Then he says the line from Gladiator, 'your wife moaned like a whore'. That was John."

After being cast as Cash in the biopic Walk The Line, Phoenix met the singer again briefly. Cash and June's poor health prevented more contact. "We talked about getting together and then June wasn't feeling well. I didn't want to interview them when they weren't up for it and insisted upon that," says Phoenix. "I didn't feel that I was really lacking in information. If anything there was too much, it was difficult to sift through."

Neither Cash nor June lived to see the finished film. She died in May 2003, followed by Cash five months later.

The film follows sharecropper's son Cash from Depression-era Arkansas through touring with rock'n'roll pioneers like Elvis Presley and Carl Perkins, to his famous 1968 concert in Folsom Prison. Along the way Cash struggles with drug addiction and meets the love of his life, June.

Phoenix was a surprise choice for Cash, not least because he lacks singing experience. He does have a reputation for shunning the celebrity side of fame, perhaps a reaction against constant questions about his actor brother River Phoenix, who died of a drugs cocktail outside a Los Angeles club. It was Joaquin was made the emergency call, his voice that was heard as the recording was played publicly in the wake of the death.

Today, in a London hotel, he's apologetic for his strange behaviour, a result of jet lag, he says. For someone known to endure rather than enjoy interviews, he's surprisingly talkative although turns down the invitation to give us a song. "I don't think you want that. I can't do it anymore," he says

Both he and Reese Witherspoon, who plays June, spent months at singing boot camp because director James Mangold wanted them to sing live on camera, rather than mime to recordings by Cash and June. It was hard for Phoenix for whom singing "was all brand new - I've always loved music but never had an understanding of it, and never had the patience or determination to really learn anything. I always wanted to and liked the idea, and listened to music a lot.

"I'd try and sing along with bands that I like but it was so atrocious that I couldn't. It was wonderful to explore Cash's music, he was such a wonderful lyricist. I have a great appreciation of him."

Nothing in Phoenix's past hinted at just how good he would be as Johnny Cash. He won a Golden Globe best actor award last week and an Oscar nomination is a certainty. Whether voters will allow a repeat of last year, when Jamie Foxx won for portraying another singer, Ray Charles, remains to be seen.

Now 31, he's been acting since he was a youngster, making his first film when he was ten. He lived in communes with his parents, members of the Children of God sect who eventually settled in Los Angeles and their five children were encouraged to go into showbusiness.

He really made his mark as an actor in three films in 2000 - Gladiator, The Yards and Quills. Since then, his credits include two M Night Shymalan films, Signs and The Village. Walk The Line promises finally to make him a fully-fledged Hollywood star.

Playing Cash was a responsibility but he didn't feel more daunted than he does by any role. "It matters a great deal to me, it's not just a job in that sense," he says.

"I always really care about the film and the character and want to get it right. I have high expectations but this one, certainly, I had a lot of doubts. You have varying degrees of doubt always when you make a film. In some sense, it's always a new process. There are so many things that you have to learn. I always feel like it's my first movie.

"With this one there was so much to take on. We prepped for six months and I still felt I'd like more time, just because there was such a searing honesty and authenticity to John's music and to his life.

"It was important to capture that. I didn't want to just make a movie. We wanted to be true to John and June's spirit and to their experience."

As for the Oscars, Phoenix hates the idea of competition, of saying one person is better than another. "It's difficult when so many wonderful films are overlooked because they simply don't have the financial backing to campaign. So there are mixed feelings in terms of awards," he says.

What it does mean is that people are having an emotional reaction to the movie which is affecting them way beyond thinking it was a good picture. "That's nice and means so much for a movie that almost didn't get made, that was nine years in the making and that every studio turned down until it finally found a home at Fox. I hope that it inspires other studios to make movies that have a story that matters," he says.

"It means that I've made a film that's resonating with people. Audiences respond to a story, real characters and authentic emotion. I hope it'll help other films get made."

* Walk The Line (12A) opens on Friday.