On screen it is clear how keenly Noomi Rapace inhabited the role of Lisbeth Salander in the film adaptation of Stieg Larsson’s Millennium trilogy.

Her bracing, brooding performance in the first film, The Girl with the Dragon Tattoo, propelled the unknown Swedish actress out of a steady career in Scandinavia into the global spotlight and was enough to convince Guy Ritchie and Ridley Scott to cast her, respectively, as the lead in the coming Sherlock Holmes sequel and the Alien prequel, Prometheus. US critic Roger Ebert was moved to write that Rapace’s Lisbeth “is as compelling as any movie character in recent memory”. She wasn’t always such. Larsson’s three novels, published posthumously, focused on campaigning journalist Mikael Blomkvist as much as the psychologically damaged hacker Lisbeth. And when filming began neither was anticipated to capture the world’s imagination. They were solid characters, yes, but not superstars.

Larsson’s books became bestsellers, The Social Network’s David Fincher chose to adapt the films for Hollywood and three accomplished Swedish films (they also played as a TV miniseries in Europe) became, unexpectedly, worldwide box-office hits. Rapace had been in the eye of this storm, trying to protect herself in what she regarded a bubble as the Swedes shot the three films consecutively with only a four-week break between Tattoo and second instalment The Girl Who Played With Fire. The actress says with a sigh she is glad it is all over: “Lisbeth was inside me for 1 1/2 years.” She needed to be expunged. Rapace describes herself as a robust person who is never sick, but immediately on finishing the final scene in the trilogy, as the crew packed up and producers began popping the champagne corks, Rapace bolted to the lavatory. “I was throwing up, kneeling on the floor and I couldn’t stand,” she says. “I was in there for an hour. It was so weird, it was like my body was throwing Lisbeth out and I was done. I was definitely done.” She thought she “looked like a f . . king freak” with Lisbeth’s mohawk, tattoos and piercings. “I remember coming home and looked in the mirror and said: ‘Who are you? What have you become?’ ”

Rapace, who began acting as a teenager after a brief film role when she was seven, admits characters “take a lot of space in me . . . after a while it becomes a mix between me and the person I’m doing, so when I’m done it’s really strange. I don’t really know who I am any more because I have been somebody else for such a long time.” After inhabiting Lisbeth Salander, that could be an issue. Lisbeth’s journey through the three films is a complex one. She begins as a disturbed but brilliant orphan, moves through awakening and revenge, and ultimately, in the final, just-released film The Girl Who Kicked the Hornet’s Nest, takes on almost a strange form of melancholy.

She is an aggressive character, a bisexual who inflicts some devious punishment on bad men. Larsson said in interviews before his death he based Lisbeth on what he believed the fiery, young, fictional Swedish character Pippi Longstocking might have become as an adult, if everything went as badly as it perhaps could. Rapace was born to a Swedish mother after what Rapace describes as a short love story with her Spanish father. Her mother met an Icelandic man and they lived in Iceland for a couple of years when she was four. She says she didn’t know her birth father. “I met him only a couple of times,” she notes. “He died a couple of years ago.” Rapace is an easy interviewee, talkative, chuffed at her present circumstances.

The actress began with her own “kind of creative picture of who [Salander] was” and what she needed to do to become her. She told her first director, Niels Arden Oplev (Daniel Alfredsen directed the second and third films), she wanted to lose weight, don the tattoos, cut her hair and “be more boyish, more masculine”. She began kickboxing and felt “like I was waking up some aggression and some dark demons in me. I felt Lisbeth growing in me and taking over more and more and my body was slowly transforming into her”. She realised the transformation was becoming complete when preparing for her motorcycle licence. She was driving as aggressively as Lisbeth would. “I was driving in a way that Noomi wouldn’t have done,” she says.

Rapace doesn’t employ method acting in its traditional form, but there is so much intense preparation the character is absorbed. Consequently, she doesn’t have to think or analyse anything when she’s working. Lisbeth became instinctual and Rapace’s family life suffered, she says. “My husband asked me a couple of times, ‘How far are you going, Noomi? How long are you going to be there because I don’t know who you are any more.’ I was like, ‘What do you mean? Do you want to pick a fight?’ I think I was a pain in the arse to be with at that time, to be honest. But that’s the way I work and the people around me know that. I don’t want to have distance to my characters; I want to break through the characters. I can’t just leave my character at work and go home and just be me because it’s like the character doesn’t exist.”

The final film leaves Salander and Rapace in a mellow place. For most of it, Salander is viewed recovering in her hospital bed as Blomkvist makes things happen. It concludes quietly compared with the first two films, particularly for Lisbeth. “I think Lisbeth is more humble at the end of this movie,” Rapace agrees. “She accepts the fact she needed help in order to become a free person and she has to accept Mikael’s friendship and love in a way. I think she begins to realise life doesn’t have to be lonely, you can have people around you and they don’t have to get you down. She’s becoming an adult.”

Nevertheless, I suggest, Lisbeth’s darkness will prohibit her from being cast in romantic comedies any time soon. Rapace laughs in agreement before revealing she has been reading potential roles “that are close to romantic comedies but not the Jennifer Aniston type”. She is not convinced, though, she has completely dropped Lisbeth Salander from her being. “I’ve been quite surprised reading them thinking, ‘What is this? Can they really see me in this part?’ ”

The Girl Who Kicked the Hornet’s Nest opened on Thursday.