Sam Rockwell: A wild card's world of pain

Sam Rockwell has a reputation as a live wire, an American firecracker. The 42-year-old actor has played a handful of major leads – most notoriously, the possibly delusional game-show host Chuck Barris in George Clooney's wildly eccentric Confessions of a Dangerous Mind. And in 2009 he scored a personal best, playing opposite himself as an existentially troubled spaceman in Duncan Jones's acclaimed Moon. But Rockwell is still often found as a second stringer – amid the support casts of The Assassination of Jesse James...and Frost/Nixon, or playing a brattish villain in Iron Man 2, even upstaging Robert Downey Jr with sheer showboat obnoxiousness.

I meet Rockwell to talk about his new film, Conviction, out today. In this soft-focus true-crime melodrama, Rockwell plays a working-class hell-raiser who gets into fights, does impromptu strips in bars and gets landed with a murder rap. The character Kenneth Waters – who died shortly after the events recounted – is a weightier, more sombre version of the several extreme cases that the actor has played in his time. Rockwell has incarnated his share of loose cannons – notably a manic lifer in The Green Mile – as well as variously sleazy and volatile galoots such as a motormouthed huckster in Ridley Scott's Matchstick Men. He also has a penchant for cartoonish comic parts – hence his twin-headed alien in The Hitchhiker's Guide to the Galaxy. He even lent his voice to the CGI guinea-pig comedy G-Force.

But what could emerge in the long run as Rockwell's forte is ordinary neurotics, like the sex-addicted anti-hero of Choke (2008), based on Chuck Palahniuk's novel.

He once said that "the key to any juicy character is to look for low self-esteem". "I think it's a humbling beginning. I do think, juicy characters, you have to start from a place of pain, you know?"

'Conviction' is out today.