Favorite actors

Whether it be on TV or in the movies, who are some of your favorite actors and why? Is it because the roles that they have starred in, or just their character in general? What makes them your favorite, and have you ever had an actor you really liked but started to hate after some time because they kept doing stupid stuff (*cough* Shia Lebouf *cough*)? Also maybe your favorite actor is a Youtube star, they do some acting as well I suppose. :p