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.

You get a role like this in a big action movie [like Jack Reacher] and you can go one of two ways: you can paint in broad strokes, which happens a lot in action films, or you can get very detailed.

The director, Moisés Kaufman, just received the national medal of the arts from President [Barack] Obama . He wrote and directed The Laramie Project and he has directed several Pulitzer prize-winning plays. He's a pretty profound director in the theater.

[Jack Reacher] is the longest I'd ever shot anything - and let's be clear, this is my first studio feature film - so there was a huge learning curve.

I had just come off of doing a play in Los Angeles which actually got me the role. It was called Bent and it was at the Mark Taper Forum. I was playing a homosexual in 1930 to 1934 Berlin who is eventually put into a concentration camp for the second half of the play. I had lost about 38 pounds for that.

Obviously I was talking to my parents and my girlfriend all the time, but it's one thing to finally be in the same room and get to be with each other and just hang out.

When I did Casual, I just let myself put on weight because he's a schoolteacher. He's not meant to be muscle-y.

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

It's pretty tough on your loved ones to try to get back into a rhythm, especially when all you want to do is do nothing.

I want to make sure everything has my 100%.

[ Tom Cruise] that kind of employee that's first to arrive, last to leave.

Psychopaths don't have that charming skill set. They definitely manipulate, but they do it through focused, unskilled means. They're more obsessive.

I had heard that Tom [Cruise] was the same way, that he is incredibly dedicated. I was very excited to meet him and I was, honest to God, weirdly surprised that the guy makes me look lazy. I think he does think I'm a hard worker, but he makes me look like I'm doing nothing. The guy is at the gym before anybody in the morning.

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

My character is called The Hunter. He's the main antagonist in the movie. In a nutshell, he's a slightly deranged natural born killer who's weirdly determined to succeed at his job, whatever his employment is. He's a mercenary and there's a high body count for him in this film [Never Go Back].

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.