After a run of sympathetic roles, distinguished Spanish actor Javier Bardem is playing an icy psychopath in the Coen Brothers' latest film. He tells Donald Clarkeabout the difficulty of staying in character, the lure of rugby - and the embarrassment of a bad haircut.

JAVIER Bardem scatters charisma the way a Basset hound sheds hair. Even if the Spanish actor, now a bronzed 38, had no talent, the warmth of his personality alone might have made him as a star.

As it happens, Bardem also has a gift for investing even the dullest line with buzzing energy. Watch him as the doomed poet in Before Night Falls, the brave quadriplegic in The Sea Inside or the compromised detective in The Dancer Upstairs. The surfeit of personality positively oozes from the screen.

It is, with these performances in mind, all the more chilling to behold the hollow, icily introverted psychopath he has created for the Coen Brothers' stunning new thriller, No Country for Old Men. Anton Chigurh, a Mexican hitman, who wears his hair like Moe from the Three Stooges, pads about Texas using a compressed-air gun - the sort deployed in the slaughtering of cattle - to annihilate anybody who dares inconvenience him.

"That sort of part stays with you in a way," Bardem says. "Some roles I have done have great souls and you want them to stay with you. When you are Chigurh you do want that guy to stay with you after filming. At first I was doing fine. Then I realised, after two or three weeks, I was becoming totally isolated. I became emotionally detached from my feelings. Remember I was also a foreigner, shooting in New Mexico, so that added to it. I would spend days without leaving my home."

Josh Brolin, who plays the unfortunate cowboy Chigurh pursues, eventually realised that his buddy might be losing a sense of proportion. "Josh, who is such a great guy, saw what was happening and said: 'Come on. Move. You've got to get out of this.' I had felt I was fine, but then realised something had gone badly wrong."

Bardem, a friendly man with a ribald sense of humour, is among the least pretentious of actors and it is, thus, somewhat surprising to hear him indulge in this class of professional angst. Acting is all just pretending. Isn't it?

"It depends upon the mood you find us in," he laughs. "We actors often hate other actors saying how hard the job is. Is it really? Give me a break. But there are things that are not easy. I was lucky to have Josh to pull me out. I may have been a little bit harmed by it. I began to feel not myself. I am usually a very social guy, but I just stopped being like that for a while."

It is slightly surprising that Bardem allowed the job to get him down in this way. After all, he comes from a thespian family and will have seen at first hand how actors shake off Lady Macbeth or Uncle Vanya when they arrive home for supper. His grandfather, Rafael Bardem, was a prominent movie star in the 1940s and 1950s and his mother, Pilar Bardem, remains a familiar face on Spanish television.

Despite this impressive heritage, Javier (born in Gran Canaria, raised in Madrid) initially spurned the stage for the life of a painter. But blood will out. One day the budding bohemian secured a job as an extra on a movie. Then he was offered a few lines. Drama College followed and, as casting directors began queuing up, he was forced to abandon any attempt to become the next Picasso.

"I found the way to express myself through acting rather than painting," he says. "I have regrets about not painting anymore. But I still like to draw my characters. It helps if you have some idea what shape they are."

Painting aside, Bardem's other great part-time enthusiasm is for the least Spanish of team games. He is, indeed, the answer to a popular movie trivia question: which Oscar-nominated actor played for his country's national rugby team?

"Yeah, my brother, who is six years older than me, started playing and took me to see him when I was nine years old. And since then I have played. I wasn't big enough to play as a prop, but I was crazy enough to give it a go."

Javier's big break came when, in 1992, he secured a role in Bigas Lunas's agreeably decadent Jamón Jamón. Playing an aspiring bullfighter who falls for a teenage Penélope Cruz, Bardem managed to reveal enough of his irresistible charm to gain a degree of celebrity in his native country. Like so many actors, he claims that, if the work remained challenging, he could live quite happily without the accoutrements of fame. Do we believe him?

"I find all that stuff totally absurd. But I don't complain. An actor needs an audience. You need to be recognised in that sense. But in this world we are living, fame is sometimes the only thing some people want. That's sad. I don't find anything exciting about it. It goes against your work. The fun of being an actor is to look and translate what you see into characters. But if other people are looking back at you, you can't quite do that."

After securing an Oscar nomination in 2000 for Julian Schnabel's Before Night Falls, in which he played the Cuban poet Reinaldo Arenas, Bardem found himself under even closer scrutiny from the world's film fans. He has, however, been cautious in his choice of English-language parts.

"I am a guy who lives and works in Spain, but sometimes there's just not enough work there," he shrugs. In 2004 he took a small part in Michael Mann's Collateral and, a few weeks after finishing No Country for Old Men, he began shooting the lead role in Mike Newell's upcoming adaptation of Gabriel Garcia Márquez' Love in the Time of Cholera.

But it is his performance in the Coen Brothers film that has really anchored him in the mainstream. The relentlessly grim, darkly funny picture, adapted from a Cormac McCarthy novel, begins with Brolin's wry Texan happening upon the aftermath of a failed drug deal. Picking through the debris and rotting corpses, he finds a case full of money and, not quite breaking a smile, heads for home. Unhappily, the bag has a transponder attached within it, and Chigurh is soon on his tail.

Fans of McCarthy's sombre novels will not be surprised to hear that the picture is unlikely to be mistaken for Happy Bunny's Happy Time, but they may still be impressed by the untempered hopelessness of its denouement.

"That comes from the book, and the Coens were very loyal to the book," Bardem says. "This is the world today. The White House is trying to tell us that we are the good guys and we are going to kill the bad guys. But horror is horror wherever it comes from. They have created an illegal war, but horror only breeds more horror. You can't fix any situation through violence. Look at Chigurh. If you create that sort of violence, you may never destroy it."

No Country for Old Men has already done powerful things for the reputations of all involved. After half a decade spent treading water - consider, if you can be bothered, Intolerable Cruelty and The Lady-killers - the Coens have received some of the best reviews of their careers and Bardem is currently an unbackable favourite for the best supporting actor Oscar.

Mind you, the actor has suffered for his art. The psychological stress was one thing, but that haircut is quite another. Do they still make pudding bowls that shape, I wonder.

"Well that was entirely the Coens' idea," he says. "There is almost no physical description of Chigurh in the book. They came across this photograph in a book of dark places, whorehouses and the like, in New Mexico and Texas. There was this guy with that haircut and it seemed right."

So, did he get away with wearing a wig? "No. Once I saw the photo I knew it was right, but even if it hadn't worked I would still have been fucked. It was my real hair. There was no way to fix it. It helped tremendously that I was away from my family. But then I realised I have a web-cam on the computer I used to talk to them. They all said: 'What's that?' And I had to say: 'I know. It's my hair.'"

One can only imagine what the lads on the rugby team might have said.

No Country for Old Men opens next Friday