HE'S SAID TO BE THE BEST CHARACTER ACTOR IN THE WORLD. What do you mean, who is he?

"Anything else beyond sleight of hand is just gimmick stuff anyway, " he continues. "You just buy a magic trick."

None of this will come as much of a surprise to D'Onofrio's unexpectedly large fanbase.

They've long had him pinned down as rather magical, though more for his way with character parts than his way with cards. He is, according to one fan website, "the world's greatest character actor"; the Internet Movie Database, the film enthusiast's first-stop website, has him down as a "human chameleon".

Some of you might be scratching your head at this point. Certainly, in the days before I meet the actor, most people respond to the mention of his name with a look of incomprehension and the question: "Vincent who?" But you do know him. You just might not know you know him. So let me introduce you. Vincent - never Vince, he tells me - D'Onofrio has been the large guy in the corner of a whole host of movies big and small (around 50, he reckons) in the last 20-odd years. He's worked with everyone from Oliver Stone to Julia Roberts;

from Spike Lee to Jennifer Lopez.

Specifics? OK, in Stanley Kubrick's Vietnam epic Full Metal Jacket he played Private Gomer Pyle, the fat boy with the moon face who ends up shooting his sadistic drill sergeant and then blowing the top of his head all over the latrine. In Men in Black he's Edgar, the dungareed redneck who gets infested by an alien bug and starts slouching around Washington DC with insects spilling out of his sleeves. In the over-the-top and often deeply unpleasant J.Lo thriller The Cell he's a serial killer, Carl Stargher, who drowns his female victims in a holding tank and then bleaches their skin. Nice. And in Tim Burton's gorgeous love letter to Z-grade movie-making Ed Wood, he plays Orson Welles. You're with me now?

Yeah, that's the guy.

D'Onofrio is not a leading man by nature or choice (his choice, that is, though presumably also Hollywood's). There are the odd exceptions, though. A few little-seen indie movies, mostly; oh yes, and then there's his television series. This week D'Onofrio returns to channel five as Detective Robert Goren in Law and Order: Criminal Intent. It's one of the many American crime buy-ins alongside the likes of CSI, CSI Miami and parent show Law and Order that have helped raise the channel's profile and quality threshold in the past few years. Viewing figures too - Criminal Intent regularly pulls in more than two million viewers for channel five, which works out as a 13 per cent share in industry-speak.

In the US, meanwhile, its ratings come in at about 18 million.

Like its contemporaries, Criminal Intent is a busy, tightly plotted hour-long drama (around 42 minutes if you cut out the ads).

What makes it different is the way it is built around D'Onofrio's performance. While everyone else in the cast - his fellow cops and the people, good and bad, who cross his path - play everything straight, D'Onofrio is given the chance to have some fun. And he takes it.

He is reminiscent of a beefier John Malkovich (if you take away the mincing self-regard), moving his ursine frame around the interrogation room gracefully, even camply at times, while speaking just above a whisper. It's surprisingly compelling stuff.

He's not moving around a lot today, but the soft-spokenness is present and correct in this dimly lit room in the Covent Garden Hotel.

Outside is one of London's chicest boutique shopping areas; just a stone's throw away is Sam Roddick's upmarket sex shop Coco de Mer, nestling in between pricey clothes stores and restaurants. D'Onofrio hasn't been exploring, though. Since arriving from Monaco, where he was also on press duty, he's been cocooned in the hotel catching up with the latest trends in British comedy (he's just been watching The Office, and apologises at one point for a particularly David Brent-ian mannerism; after I leave he's got a League of Gentlemen DVD to watch). More importantly, though, he's been catching up with his rest: "I only got off work a few days ago and I'm just dying to get some sleep."

It's unclear whether his just-about-audible murmur of a voice is natural or for actorly effect, but it is complemented by a nervous cough every time he starts to essay an opinion.

He's by no means a difficult interviewee, but it seems he doesn't enjoy the experience. He says he is uncomfortable with the whole idea of celebrity. All actors say the same as a matter of course, but for once it sounds convincing.

D'Onofrio says he can talk about his work - "I have to play the game" - but it doesn't come easily. He is not, he says, a social animal. "I'm able to talk about what I do for a living because it's what I do. If we were talking about something else you might not think I was such a great talker - or you might not think I was able to talk at all, for that matter." (Maybe this also explains the 45-year-old's rather arrested teenage vocabulary. ) He's certainly never pursued a high profile.

"When I had a press agent, before I realised I didn't need one, I never asked him to do magazine covers or late-night talk shows, " he says. "Look, right now I have one of the most popular dramas on television and I have never done a late-night talk show and I won't do one - and I like those shows. I have friends who go on those shows who I find hilarious, like my friend Vince Vaughn. He's fantastic on them, and when he's on them I can't stop laughing.

There are certain guys who can do that shit and girls who can do that stuff. I can't do it, man. I'll embarrass myself and everyone else involved in what I'm supporting. I have a hard enough time walking down a red carpet and keeping a smile on my face."

Which, some might feel, would make his choice of acting as a career a curious one. It's a profession for show-offs, isn't it? "I think a lot of people see it as that, " he replies. "I'm able to have a pretty acting career - more than half of my life now - and I'm still able to mind my own business, you know. You haven't seen me on the cover of magazines or at any Hollywood parties have you?" I don't go to too many, I have to confess. "No, but you haven't seen me in those magazines and doing all that kind of crap. I have as simple a life as one could have, doing what I do."

Acting, he says, is a form of escape. Escape from what? "Life, everyday life." Does that mean he is better at acting than living? "I am, I am. A lot better."

His personal CV backs that up: he has had two marriages and two divorces.

He also has two children, one of the more successful by-products of his love life. "They're an escape from life too, " he says, smiling. "My daughter's 12 now, and thank God she wants to see me more often because she's older. Last year she came six times to see me, for a couple of weeks each time. That's a lot of quality time to be spending with your daughter and it's 24/7 because she doesn't have school when she comes. She comes and PAs on set and hangs out with me.

My son's four years old, and when I see him he's with me 24/7 as well."

Leila, his daughter, lives in England with her mother, the actress Greta Scacchi. D'Onofrio met Scacchi on the set of Robert Altman's film The Player. Their relationship was by all accounts a rather torrid one, and ended badly.

Six months after Leila was born, D'Onofrio walked out - or at least that's Scacchi's version of events. She's still burned by the whole thing.

In an interview towards the end of last year her anger was still obvious 12 years on. "It was a massive betrayal, " she told the interviewer.

"This wasn't a child I'd had against his wishes.

This was a child he persuaded me to have.

Then he changed his mind."

Today D'Onofrio is rather more circumspect about the relationship, and certainly rather more sanguine. "That was an intense, wonderful relationship and we got a beautiful daughter out of it, " he says. "I don't think I can handle anything as wonderful and intense as that again."

It's easy to fall in love with somebody that you're in love with in a movie, he adds, but one relationship with an actress was enough. "I've been interested before, that's for sure, but I'm not sure I'd do it again. I think one was plenty."

He looked outside acting for his second wife, the model and photographer Carin Van Der Donk, who is mother to his four-year-old son Elias. Unfortunately that one didn't last either. "Since my divorce, work is the main thing in my life. I was hoping it wouldn't be and then I got divorced, so when I'm not with my kids, yeah, work's the main thing."

There's plenty of it, certainly. Criminal Intent has a pretty full-on schedule, often involving 14hour days, "sometimes more". We're only up to series two in the UK, but in the US the show is on series four and D'Onofrio is halfway through a six-year contract. "As long as the scripts stay good, I'm happy, " he says. "It's a lot of work but at least we're still trying to do it good."

By "good" he means that it's not "soapy".

Television is not like real life, he says: "Our show is just straight-out crime storytelling."

He doesn't have any inferiority complex about working for the small screen either: how many good movies, he asks, does an actor actually end up doing? "I've done over 50 films, " he says. "In one's career I guess you're lucky if you do one classic, you know? The lucky ones or the really talented ones do maybe two.

What's the rest? The rest is fluff anyway."

Has he done a classic yet? "One, " he says.

"Full Metal Jacket." Not quite his first film, but near enough. He put on 70 pounds to play Gomer Pyle for Kubrick. "It was so early on in my career, I was happy as hell just to be there and not be fired, " he says.

Kubrick used to invite him and co-star Matthew Modine over on Saturday nights to watch movies with the rest of his family. "He was a good guy, man. It sucked when he died."

His performance in the resulting movie was eye-catching, even if it wasn't great. Too many shades of Jack Nicholson. "It's a young performance, " D'Onofrio says, "but it's okay."

It certainly got him noticed. Soon he was turning up as Lili Taylor's fisherman friend in Mystic Pizza, the film that made Julia Roberts a star. He's rarely been out of work since. If there was any chance of chasing fame, though, he's never pursued it. He likes the description "character actor". "It's something I'm very happy with, " he says. "There's no pressure. I grew up with actors who were the great character actors of my generation who tried to be leading men and it f-ed their careers up. I'm not sure it would be good for me. I'm able to have a great career and still be the shy kid that I was, you know?"

That shy kid was born in Brooklyn and, despite growing up in Florida and Honolulu, considers himself a New Yorker. He lives there now and spent every summer in the city with his grandfather, so he believes he qualifies. His parents divorced when he was young; nine, he thinks. "I really don't have a lot of issues with my parents' divorce. My mother was always a very positive, happy woman and remarried a great guy. And my dad could be an idiot sometimes but other times he was pretty clever."

He says he takes after his mum, Phyllis, but there's a bit of his dad, Gene, in there too - "the idiot part". Certainly Gene D'Onofrio had the bigger influence on his choice of career: he was an interior decorator by trade, but spent most of his spare time in amateur dramatics. "I would say he was a frustrated actor, yeah, " says D'Onofrio. "I used to build sets for him and run the sound for him and stuff for the little theatre companies that he had, and got to know actors. I tried to do a couple of plays that he was putting on, then realised how bad I was. It interested me even more that I was a bad actor and yet I still wanted to do it, because I'd never stuck with anything that I wasn't good at. And I thought, well, this is interesting, this is something I suck at yet I still want to do. And so I went back to New York and started studying."

His acting apprenticeship followed the familiar pattern - off-off-Broadway plays and the usual minimum-pay jobs to cover the rent - delivery man, bouncer and, it's said, bodyguard for Robert Plant and Yul Brynner. All of that ended with the Kubrick role. D'Onofrio remains indebted. "He helped establish me as a serious character actor, " he once said of Kubrick, though press him and he'll admit the director he most enjoyed working with was Robert Altman. "I always imagined him being a kind of avant-garde grandpa and that's exactly what he is, real warm with a great sense of humour. And at the same time he's a prick artist. He can be as much of a bastard as any artist can be. He's got that whole Pablo Picasso thing going on. It's an amazing combination: he makes you feel so artistic and warm.

And I was only on that set [The Player] for a couple of days."

Does D'Onofrio consider himself an artist?

"I hope I am. I feel like one sometimes. When I get up in the morning and have to go to work, the only thing that makes me feel good about the next 16 hours I'm going to spend on set is that I'm going to produce something that wasn't there before. It could suck or it could be good, but at least it's going to be my production.

You walk into a room with a bunch of actors and there's nothing there and then suddenly there's something, there's chemistry, there's things you can cut with a knife, out of nothing there's something."

The key thing about acting, he says, is doing your homework. It's all about research. For a role like Carl Stargher in The Cell, that meant reading up on the thoughts and writings of the criminally insane. During filming, his hotel suite was full of pictures and photographs, "all this creepy stuff". In truth there's been a lot of that. He's played a lot of bad guys. But he says morality - his morality - has a part to play in the characters he chooses. His bad guys never walk away at the end. "I've seen a lot of bad guys walk away in real life in my research, and I don't like it. It's not something I'm interested in doing."

The fact that his children are now so important to him might also be an influence. "These days I actually ask my daughter, 'What do you think?'" he admits. "Like, for instance, what was that movie with Benicio Del Toro and Tommy Lee Jones? You know, the killer movie?"

The Fugitive?

"No, it was another crap one, about one guy who trained the other guy and they were out in the woods."

The Hunted?

"Yeah, The Hunted. And in the original script of that, when they sent it to me, the guy was killing women. It started off with the killing of a woman and he ended up killing the woman cop in it too. And I said to them, 'I have to think about this, ' and I actually asked my daughter and she said, 'Don't you think you've killed enough women?' And I said, 'You know, you're right.' And I don't think it's nice, especially if your daughter says it to you. It's not nice any more."

So there you have it. These days, thanks to his children and television, Vincent D'Onofrio is one of the good guys. To everyone bar Greta Scacchi, at any rate.

A new series of Law and Order: Criminal Intent begins on Wednesday at 9pm on Five.