TOM Cruise seems to be shaking off his clean-cut image and showing a darker side, onscreen, at any rate.

Following his recent role as a haunted American civil war veteran in last year's Last Samurai, he now plays a cold-blooded hitman in Collateral, a performance that is shaking up his perfect smile and sex appeal.

As contract killer Vincent in Michael Mann's psychological thriller, Tom has gone for a significant career shift, playing his darkest role to date.

"I take on characters I feel are personal challenges and Vincent is definitely a role I've never played before," the 42-year-old explains.

Set in a gritty Los Angeles after dark, Vincent is set on carrying out a series of hits, taking taxi driver Max (Jamie Foxx) hostage along the way. But as the pair race through the night, they find they're on a dangerous trip which will alter their lives.

Much of the action takes place inside Max's cab and a lot of the film was shot on high definition video to lend it a more natural mood and tone.

And Tom's own look is quite different this time around - the smile is still there but there's a threatening edge, while the actor has silver-grey hair and sports a nondescript grey suit.

"Michael came up with the look and I thought it was perfect for Vincent. If someone is asked for a description, he might say, 'Medium height in a grey suit'. It describes anybody and nobody. Being anonymous is what we strived for.

"Dressing the way I did and then playing the character was about uncovering who Vincent really is and then finding that point where things start to go wrong for him."

But the role is far from a one-sided killer. This is a complex character with a back story, he says.

Cruise fans will be pleased to hear that he's back to more traditional territory next, with Mission: Impossible 3 due to start shooting soon.

But he says he wants a grittier thriller for the third instalment - although not so violent or demanding that it alienates the popcorn-munching, summer blockbuster audience.

Now that's he's single again, his career and his two adopted children Isabella and Conor, with ex-wife Nicole Kidman, seem to dominate his time.

"I have been busy hanging out with my kids and I've just been working on things," says Tom. "I'm having a good time and life is good, I've been very busy. I haven't had a break yet, but I will take some time soon."