John Leguizamo: A portrait of the artist as a madman

Baz Lurhmann's feverish musical Moulin Rouge is like a fairground ride on the verge of spinning out of control. But if you weave your way through the high-speed can-canning showgirls, you will find a performance by the wolfishly handsome John Leguiz-amo that is ever so sweet and sad. Leguizamo plays Henri de Toulouse-Lautrec, though you should banish all memories of Jose Ferrer in the 1952 Moulin Rouge (of which Lurhmann's film is categorically not a remake). The way that Leguizamo plays the artist, you can imagine him hanging out at Warhol's Factory, squeezed between the transvestites on the leather couch, giggling like a fool but doomed to remain detached from the world that drives and delights him.

It's a batty interpretation, but Leguizamo really did his homework. "Dude, I read so many biographies," he says. "This guy was a maniac. The camera had just been invented, and he dropped his pants every chance he could. One time he even took a poop for the camera." Leguizamo wrinkles his nose when he says "poop". "He was crazy, man."

Crazy is a breeze for Leguizamo. It was there in his defining performance, as the jumped-up hood Benny Blanco in Carlito's Way (1993). His nightclub showdown with Sean Penn remains that film's most electrifying scene – they're like a pair of ticking bombs, and you couldn't put money on who would be the first to explode. For a while after Carlito's Way opened, you could buy bags of Benny Blanco in dark New York alleyways: the dealers had adopted the name as slang for smack. Talk about respect.

He was ranting again in Summer of Sam (1999), as the sexually insecure Italian-American hairdresser Vinny, whose idea of foreplay was to get undressed. In a way, Vinny is insulated from his own flaws because he isn't smart enough to acknowledge them, whereas Toulouse-Lautrec knows only too well what he is, and what he will never be.

"He was such a sad creature," says Leguizamo. "He was the son of two first cousins, so he was born with all these impediments: dwarfism, a thick tongue, shins that snapped when he was a teenager. He longed for love, but women never gave him that love. Of course, he had a lot of sex with prostitutes." He thinks for a second. "So it wasn't that bad."

Leguizamo has worked with Lurhmann before – he played Tybalt as a kind of New Romantic Latino highwayman in Romeo + Juliet (1996) – and the freedom that he finds in this collaboration is clearly liberating. "Baz wants you to take huge risks, to fail as much as you can. It's refreshing to work with someone who's so brave, what with the state of movies sucking so bad."

His tongue gets stuck on the "s" in "sucking", turning the word into a dirty, insinuating hiss. Even if you have never caught any of the profane, autobiographical one-man shows which have earned him acclaim in America – shows like Mambo Mouth and the award-winning Freak – you can hear the way he relishes language and dialect. One of his tricks is to introduce innuendo into a scene, through a lascivious line reading or a curl of the lip. In part, it's a riff on the stereotype of the Latin stud, but it's also what makes him so exciting: you can tell there is always something going on in his head, even if you're not sure what it is, or whether it's decent.

At school, he was voted "Most Talkative Person." It's not hard to believe. "I was a troublemaker," he smiles. "But my teachers told me I was too smart and funny to throw away my life. I was all set to become a loser. A happy loser, but a loser nevertheless. I was working at Kentucky Fried Chicken. My teachers and my stepmom encouraged me to try performing. That was where I found myself. I felt free."

Leguizamo was born 37 years ago in Bogota, Colombia, possibly with the same wicked glint in his eye, and the same laugh that sounds like a bullwhip cracking, that he still has today. His parents moved to New York when he was four years old. "We went from this hot, bright place to this dark, dirty city. It was a shock. Now I feed off that darkness, that grittiness." At school, he loved the mix of cultures; he would hold on to that, and later make it part of Freak, in which he mimicked hundreds of voices, playing black, white, Asian, Irish, Italian.

It wasn't just his class-mates who turned up in the gnarled comic monologue of Freak. Leguizamo's father had been a tyrannical, abusive figure, a man for whom nothing was good enough. Leguizamo remembers being thrown against a wall by him; in Freak, he transforms this memory into an out-of-body experience. "Humour is the best way to deal with that shit," he tells me. No wonder he felt emancipated by acting. He worked hard at it, but some of those early roles were unedifying.

There was Super Mario Bros (1993), in which Leguizamo and Bob Hoskins played superhero plumbers in day-glo dungarees. And when I mention Miami Vice it's clear that he wishes I hadn't. "I thought of myself as an artist," he says, "and here I was doing TV." Worse, he was playing a Latin drug dealer. "The most heinous portrayal of the Latin people that I could have done."

It was Carlito's Way that showed what Leguizamo was capable of, but he realises now that he didn't capitalise on its success. "I was picky, but my managers were really picky. I turned down so much stuff waiting for that special role. I let a lot of time slip by." When he did start appearing on screen again, his hunger was palpable.

While Patrick Swayze and Wesley Snipes grimaced their way through the drag-queen comedy To Wong Foo, Thanks for Everything, Julie Newmar (1995), Leguizamo was the only one who appeared to be having a hoot with the fish-nets and slap. He became a tonic of an actor; you see that he's in the cast of the new Schwarzenegger movie Collateral Damage and you think: at least there'll be someone worth watching. The curious thing is that movies aren't so important to him now. He has a new one-man show opening on Broadway next month. "It's gonna be tough because I've got to find the dirt on my present relationship. It's gonna kill my girlfriend to see that on stage."

What do you mean "got to"? "To be true to the piece. You can't just show the shiny gold parts. You have to show the tarnished rusty underbelly. I used to be really brave that way and say the wildest stuff, but now I've got something to lose." He has. Two children, for instance – a 10-month old son and a two-year-old daughter. Benny Blanco has finally had to put down his gun and learn to play nice.

"I used to need to act," he says. "I needed it like air. Not any more. Now the only Oscar I care about is the one on Sesame Street."