Severus Snape
Contrast is, perhaps, the strongest element in any art. What is the whitest of the whites without the blackest of the blacks to define them? Light and dark so carefully juxtaposed against one another is that which draws us into the depths of a work of art. Contrast fools our sense of the two-dimensionality and tricks us into believing a painting or drawing to be part of our own space and indeed part of our own reality.
In literature and film there can be no protagonist without the antagonist as balance. The best heroes are only best because of their contrast with the wonderful villains who oppose them. Severus Snape was the impetus that sent Tom Riddle hurtling towards James and Lilly Potter and is just as responsible for the future of Harry as anyone. Severus's hatred of his old school tormenter who would marry the girl of his dreams would almost seem to justify his disdain of the boy who lived. Of course Severus in the end was not truly bad at all. He was the most faithful servant of Albus Dumbledore who did everything that was asked of him and Harry Potter called him "the bravest man I ever knew." Fortunately we do not know this until the end when he looks upon the eyes of Lilly Potter one tragic last time. Voldemort may have been the blackest of the blacks of the Harry Potter series but it was Snape who provided my chapterly fulfillment of contrast.
No one could have portrayed Severus Snape better than Alan Rickman. It takes quite a talent indeed to illustrate so much depth with so few words. I used Mr. Rickman's face for my pot because of this.