I always think it's the true test of acting when someone can put on a real convincing accent. Probably really bad accents slip by me if I'm not a native of that accent, because I wouldn't know the difference. For example, I might not notice if an actor had a bad Australian accent. But Peter Sellers' American accent in Dr. Strangelove was perfectly transparent to me and I understand that Collin Ferrel's American accent is faked. That's impressive. What actors have the ability to put on great accents, and what roles showcase this ability to a high degree?