I change myself a lot. Some roles you don't want to be big, bulky, muscle-y guy and some roles you want to be a lean, marathon-runner physical type. And some roles you just don't want to be in shape.

I'm not a method actor but it certainly does help to have that kind of dedication. I treated my preparation like I was in the military. I didn't go out ever. I went out for drinks probably twice in five months. I lived very monastically.

I only had a three-week break from the beginning of Bent, so I went from one thing to the next. I got back [from shooting Jack Reacher] and there was a sense of, "Oh my God, what do I do now?" I don't have personal trainers around me all the time, I'm not on a meal plan, which I had been on for almost a year straight. There was a lot of sleeping.

The role I played [in theatre] was originated by Ian McKellen in 1979 and he came. I didn't know he was there and I walked out at the end of the play, which is a very intense play - my character is required to do some really horrible things - and the director was waiting backstage and he goes, "Obviously I didn't want to tell you guys, but Ian was here today" and we, of course, freaked out.Ian McKellen said some really beautiful, kind things, one of which was, "It's so much harder to watch than it is to do."

When I came on to Jack Reacher, I had just taken my girlfriend on vacation and ate everything I could. I put on about 15 pounds, so when I met [the Jack Reacher team] I was clocking in at about 180. They looked at me and were like, "You're just gonna lose five pounds, we're gonna keep you skinny".

I read as many books about the psychology of a psychopath as I could and I researched what exactly happens to soldiers.

I'm a trained actor and I can always tone it down, I can always simplify the work I've done. But if I'm asked to bring the nuanced and complicated work, I'll have it in my pocket, and all that information helps.