Q: How did you research your Kick-Ass role? Were you familiar with the original comic-book series?
A: I wasn't into the comic books before I got the role. When I got the job, I was in New York filming something else, so I went down to a massive comic-book store—Planet Comics or something—and there were only three issues out at the time. But I literally based the character off of those. The way they were written, the way he spoke. He's a nobody at school and has only two friends. He hasn't got a mum. And he creates this different person.

Q: The comic-book character is a blond guy.
A: I suggested to [director] Matthew [Vaughn] that I dye my hair because the character is blond. And he said, "Yeah, Aaron, have you ever seen Colin Farrell in Alexander? We're not fuckin' dyeing your hair." He's pretty straight to the point, Matthew.

Q: The violence in Kick-Ass is pretty intense.
A: I've never seen action and violence that brilliant in any other film—so raw. And the madness of it all. It's a complete dark comedy. You're kind of in horror of it, but at the same time, you're laughing your head off because it's so mad. A young girl stabbing people and chopping their legs off? It's just brilliant.

Q: You won't see that in Spider-Man.
A: And if you think about Spider-Man—how he was introduced—he was, like, a high-school or college kid, but, really, the actor is about 30. But Matthew has gone and put real kids in costume. We were, like, 17. Chloë [Grace Moretz, who plays Hit Girl] was, like, 11. So the idea of superheroes who are the ages they look in the comic book—it's mental. It completely takes the piss out of superhero movies.

Q: How did you perfect your American accent?
A: I had a coach on set for the accent. I lived in L.A. and New York for about half a year before we started filming, so I was working on it, kind of picking it up. We filmed a lot of stuff in studios in London, my hometown, so it was hard to maintain the American accent surrounded by British people.

Q: Your next film, Nowhere Boy, is a biopic about a young John Lennon. Seems like a lot of pressure.
A: There's no footage of that part of his life, so it became our mission to tell the story with justice. We had this sense that, when you watch the film, you shouldn't go, "Oh, that's John Lennon." You should go, "Okay, who is this boy?" And then you start to progress and understand who he becomes—more and more like the person you start to recognize.

Q: And you did all your own singing and guitar playing?
A: Yeah. I had a private guitar trainer. I'd sit with him for three hours every day and play and sing. I learned banjo and guitar. It was good fun. I'd watch footage of Elvis and try to copy him. I recorded about 20 different songs for the film. I think they used about five.

Q: Everyone is obviously interested in your relationship with Sam Taylor-Wood, 24 years your senior. You two are engaged and expecting a child.
A: We'll get married once Sam can feel comfortable enough to get back into a dress. We've got plans, but that's something we'll keep to ourselves.

Q: Your baby is due this summer. What are you looking forward to most about being a father?
A: The whole experience—to watch my child grow up, everything from Day 1. It's hard to explain. I can't wait.

Q: Has the age difference between you and Sam ever been difficult?
A: She's wonderful. If you ever see us together, you wouldn't even see a difference. I love her, and it's true: We have this wonderful connection. It's nice. I'm happy.