Sean Penn. Wow, who knew Spicoli from Fast Times at Ridgemont High would turn out to be a serious actor, let alone one of the best actors of all-time? My favorite of all his roles has definitely been in I am Sam. I loved that movie. Penn, who can come off as being a complete jerk at times, played a truly sympathetic and sweet character who was more than believable.

By now, you should know that my criteria for who makes the cut as the best of the best hinges on versatility. Sean Penn is one of the most versatile actors. As mentioned, going from goofy surfer characters to pompous tough guys. Who he is in real life, we don't know and I think he likes it that way.