Sam Rockwell: Almost famous

Sam Rockwell's been a well-kept secret for years. So when George Clooney decided to cast him in 'Confessions of a Dangerous Mind', the studio was horrified. Ryan Gilbey meets an actor who wonders what he has to do to make it

Two days before I meet Sam Rockwell in London, he calls in at the Berlin Film Festival to collect the Best Actor award for his portrayal of Chuck Barris, TV-game-show innovator and possible CIA assassin, in Confessions of a Dangerous Mind. The film, directed by George Clooney and written by Charlie Kaufman (Being John Malkovich, Adaptation), fizzled out at the US box office, but has generated a low hum of respect. I congratulate Rockwell on the prize. The recognition must be fulfilling, I suggest – it's the kind of small-talk you offer while the cigarettes are being lit and the tape recorder starts rolling. But this chit-chat stumps him momentarily. "Uh, yeah, I guess," he mumbles. Do I spy disquiet? A dissatisfaction with the practice of judging actors like racehorses? I tell him he sounds ambivalent about the award, and he promptly rights himself. "No, man. Not ambivalent. Just tired."

He isn't the first jet-lagged star who has flown into town with scarcely the energy to flash his passport at immigration, and he won't be the last. What makes Sam Rockwell different is that he isn't willing to hit the canvas just yet; clearly, the show must go on. Waiting outside his hotel room for the previous interview to finish, I hear him compliment his inquisitor. "You're lovely," he tells her. It isn't the words that strike you so much as the slurred voice – the lips too lethargic to part properly, the jaw audibly rusty. And still he is cranking up the charm.

He has postponed his lunch-break to see me. And while it's disconcerting to hear him haggling with the PR in my presence over the duration of that break ("Was it always an hour-fifteen? I thought it was an hour-thirty"), no one could accuse him of lying down on the job. He's constantly up, out of his chair, bounding around the room, acting out scenes from the film to illustrate a point. It is, more than anything, a performance.

No news there – if we're honest, we are all of us on set, in close-up, most of our lives. But the stamina it takes is consistent with what we know about Rockwell. This 34- year-old actor has waited quietly for success. There were early bit parts (a thug in Teenage Mutant Ninja Turtles, a hanger-on in Last Exit to Brooklyn) but it was a full eight years ago that he got his big break in Tom DiCillo's Box of Moonlight, where he played a nature child in Davy Crockett furs who liberates a working stiff. No, I wouldn't rent the video either if I knew the plot in advance, but listen – Rockwell can take a Robin Williams "inner child" role and make it impudent, unapologetic, even borderline-unwholesome.

The important thing is that he really hung in there. He is arguably as good at waiting as he is at acting. Box of Moonlight was his only after DiCillo had resisted pressure to cast Johnny Depp or Jason Priestley. And then Rockwell still had to sit it out while the budget came together, all the while keeping his hair long. "If I got a job playing a cop or something, I'd ask Tom if I could cut it and he'd say: 'Yeah, but not too short. We might get the money soon.' Things went on like that for a long time."

Three years, in fact. It was a sweet cookie of a film, but no one wanted so much as a nibble. "I think maybe 20 years from now, people will look back on that movie and..." He doesn't finish the sentence.

He has been busy ever since. He was an aspiring crook outwitted by Gene Hackman in David Mamet's pared-to-the-bone Heist. "Boy, that was a lot of testosterone on one set. I mostly hung back. Hackman and Mamet are powerful horses. Very masculine. They're into telling dirty jokes and hanging out. Mamet and I mostly talked about boxing. It was fun."

He keeps coming back to that word. His spot as eye-candy-turned-bad in Charlie's Angels was also "fun". We don't get around to discussing his lovely work in Galaxy Quest, but I'm betting it was fun.

As was his cameo as a gay bellhop taunted by Vince Vaughn in Made. He and Vaughn met at a charades party at the latter's house, and have been tight ever since. "Actually, it was running charades," he says quickly, correcting himself. "It takes place on different floors of the house. It's a little more active than regular charades."

Rockwell's reward for his patience is Confessions of a Dangerous Mind – his first lead in a mainstream-ish picture. It's a moving performance – or rather a not-moving one, since he is the still point around which the rest of this crazy-headed picture spins at increasingly high speed. It's not at all the kind of trick we're used to seeing him perform. To date he has more commonly served as the jump-leads that will kick-start a sombre set-up. He moved like an orang-utan as the caged serial killer in the death-row drama The Green Mile, and was the only cast member who you didn't want to end up frying in the chair. He has a certain volatility. Liable to make a song and dance. Not to be trusted with scissors.

Which is why his take on Chuck Barris is so inspired: the mania is there, only this time it's focused inwards. Rockwell's Barris is an innocent Mama's boy ripe to be surprised by anything – the wacky world of 1960s television, his own boundless imagination, Drew Barrymore's sexual promiscuity, Julia Roberts as a hard-shelled femme fatale who hisses like a cockroach. And that's before he starts moonlighting from his day job as creator of The Dating Game and The Gong Show to perform hits for the CIA in West Berlin side streets. Barris's grimly funny 1984 book is written in the hardboiled patter of dime-store noir, and Rockwell is absolutely faithful to the gag; he has, at last, mastered the role of straight man. This time, for the first time, he sends the audience home asking questions, rather than just panting for breath.

"It was a strange job to get," he muses. "Charlie's screenplay read like Inspector Clouseau meets Martin Sheen in Apocalypse Now meets Elvis Presley meets Travis Bickle. But George and I decided to make the tone more like Dr Strangelove meets Carnal Knowledge – something with a juicy dramatic undercurrent.

"As an actor it was hard to know what to make of it all. You're saying these insane lines. 'I'm not killing people – my future's in television.' That's hilarious stuff, man! How am I gonna say that? It's ironic. It's Kubrickesque. Charlie wrote it very tongue-in-cheek. But I decided to play it very real, very organic. I didn't want to poke fun at the guy. I imagined I was just in some straight biopic."

You can't help feeling sorry for Rockwell, despite his success with the movie. Even after all these years he has to fight for everything. Clooney always wanted him to play Barris – the two had worked together a while back on the heist comedy Welcome to Collinwood, which is only now getting a UK release on the coat-tails of Confessions. But, as with Box of Moonlight, other names were considered more bankable. Edward Norton, Ben Stiller and Johnny Depp (again) were all in the frame at some point. Executive producer Harvey Weinstein needed convincing about Rockwell. When Rockwell tells me this, I nearly leap out of my seat. But Harvey loves you, I splutter in a most unprofessional manner. He said so in print!

"I know, I know," Rockwell smiles. Back when Box of Moonlight was being rejected by the Cannes selection committee, Weinstein had gone on record as saying about Rockwell: "He's a movie star". "George showed him that article. But Harvey still wanted me to do a screen test. We did the whole Scarlett O'Hara deal – lights, costumes, everything. Usually they just shoot it on a video camera. George pulled out all the stops."

I ask how it makes him feel, to still be at the point where he's trying to get noticed, but he dodges the question in a way that makes me feel I shouldn't have asked it. "You just have to tell yourself it doesn't matter." Nevertheless, I feel irritated on his behalf that the paperback reissue of Barris's book neglects to mention him. Brad Pitt's name is there, though his entire contribution to the film amounts to a 3-second cameo. But no Rockwell.

He should worry. He's just finished shooting his biggest picture yet – Matchstick Men, a comic thriller directed by Ridley Scott in which he plays sidekick to con-artist Nicolas Cage. Scott cast him after seeing six minutes of rough footage from Confessions.

"My character doesn't do a lot. There's no wacky hair, no accents. Just me and Nicolas ad-libbing. It was the easiest job I've ever done." He breathes a sigh of relief so richly felt that it might have been building inside him for the past eight years.

'Confessions of a Dangerous Mind' is released 14 March. 'Welcome to Collinwood' is released 25 April