All cheap and debonair

Talk to me about supporting characters. When you're supposed to fall for the heroine, and instead it's the second spear-carrier from the left who turns out to have the thorniest moral dilemma or the most fascinating backstory. This happens to me all the time; I can't be the only one. So who are your scene-stealers? Movies, books, operas—your own work—which character roles do you remember long after you've forgotten who played the protagonist?

(This post brought to you courtesy of Eleanor Cameron and L.M. Montgomery.)