If you need evidence of Stellan Skarsgård's versatility as an actor, look no further than his forthcoming releases. The ubiquitous Swede stars in a British horror picture called WAZ, an edgy, urban tale that rummages around the very darkest corners of the human psyche and demands a bloodily literal answer to the question: what would you be prepared to suffer to save the one you love? Skarsgård's other movie is the polar opposite to WAZ's grim thrills. He plays one of three male leads (alongside Colin Firth and Pierce Brosnan) in a sunny adaptation of the hugely successful Abba-themed musical Mamma Mia.

Shooting for WAZ required Skarsgård to spend around one week naked and covered in prosthetic wounds in a grotty warehouse in Northern Ireland. “It was disgusting, and it wasn't a very pleasant location either. It's better to be naked and covered in blood in the Bahamas.” However, shooting Mamma Mia involved singing, dancing and donning lurid costumes. “When we get into the spandex suits with the platform shoes, you don't know whether you want to shoot yourself or just continue to laugh. It's very funny.”

Despite being Swedish, Skarsgård claims he rather missed out on Abba the first time around. “Of course I was aware of them. The thing was to try and avoid them. But then I did the film and I realised that the music was more intricate than you think. You can listen to the songs over and over and hear new things all the time.”

Skarsgård is not quite the household name that his Mamma Mia co-stars are - along with Firth and Brosnan he plays one of three potential fathers to a girl whose uncertain paternity is solved through the medium of Abba songs. Meryl Streep plays her mother, good-naturedly getting into the spirit of a character who evidently sowed plenty of wild oats in her early years. Skarsgård is clearly amused by what he describes as the “top-heavy casting” of this feelgood flick, which also stars Julie Waters and Christine Baranski; and by how unexpected a film it is on his own CV. “It's not like they went, Mamma Mia - we've obviously got to get Stellan. I have never sung before. But I had so much fun doing it.”

But while his name might not ring quite so many bells with the average movie-goer, his face certainly does. That's him, peering mournfully out from behind a layer of prosthetic barnacles and seaweed as Bootstrap Bill in the second and third instalments of the Pirates of the Caribbean series; he's a show-stopping Viking warrior in the otherwise forgettable Clive Owen vehicle, King Arthur; he played Father Merrin in two Exorcist prequels and has collaborated with the Danish director Lars von Trier on three projects.

Skarsgård is an actor's actor. He's a seal of cinematic quality on a film - his presence in WAZ allows the audience a flicker of empathy for a character in a film populated by the damaged and the damned, and it brings the film a melancholy, flawed and very human soul where it might have descended into the kind of torture porn that currently blights the horror market.

In the flesh, the 56-year-old cuts a striking figure. He's well over 6ft with a growl of a voice and a dry humour. He can be lazily flirtatious, but he's also outspoken and very serious about what he perceives as the threats facing cinema, and the arts in general, in today's rapaciously consumerist society. Skarsgård is generous with his praise for other actors: Meryl Streep's singing is “wonderful”; of his co-star in WAZ, the former rapper Ashley Walters, he says: “I fell in love with Ashley immediately. He has a fantastic future on the screen. He has a very sensual face that photographs beautifully.” But a professional since his teens, he's intolerant of what he considers bad behaviour on set. Skarsgård asked one Hollywood actor - he won't say who - to explain to him how he was going to repay him for arriving 20 minutes late on to the set. “He wasn't late again,” says Skarsgård with satisfaction.

Despite nearly a lifetime of experience as an actor, Skarsgård says he is still plagued by anxieties about the job. “Fear. It can be devastating. A lot of energy goes to not being afraid.” Fear of what? “It's the combination of you want to do something good, and to do something good you need to have a high intensity, but at the same time be totally emotionally relaxed so you don't block yourself. There are a thousand reasons to be paralysed with fear on a stage or in front of a camera. There are very few reasons not to be afraid.”

Skarsgård started out, aged 10, in amateur stage performances. He got his first professional theatre job at 13, and by 16 he had a role in a TV series. “We just had one channel in Sweden back then so you became famous immediately.” His international film career was launched by his performance as Emily Watson's quadriplegic husband in von Trier's Breaking the Waves in 1996. He considers the director a close friend; they share a similarly dark sense of humour. Of von Trier's recent struggle with depression, he says, “I had hoped that Bergman's death would cheer him up a little, but no.”

So what was the experience of Pirates of the Caribbean like for someone whose heart remains rooted in theatre and independent cinema? “Gore Verbinski is interested in acting, so you never felt trapped in the technicality of it all. The scariest thing was the press junket. That scared the shit out of me because that was a machine that could have supported half of Africa for a year.”

To escape from the more excessive side of the film industry, Skarsgård says he lives a very normal life back in Sweden. “I do the shopping, I do the laundry. I cook. I've got a lot of kids and friends and family.” He's not joking about the kids - there are six Skarsgård offspring, five boys and one very tough little girl. The two oldest boys, Alexander and Gustav, have followed their father into acting. They're both very good, reports their father, adding proudly, “and I hear also that they behave properly on the set. The only ambition I had for them was to make them nice people.”

WAZ is on selected release on Feb 22; Mamma Mia is out in July

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