One of my jobs as an actor, regardless of who I play - even if I'm playing a despicable character - is to make people think that that character could exist, that he's real, and the way to do that is to make him believable. He doesn't have to be likable or charming, but he just has to be believable. That is someone who I could see on a bus. That is someone who I could walk past in the street.
