I think you have to be crazy not to want to work on the Joker! I can't think of many characters, heroes or villains, that are as malleable as him. He really can be interpreted in so many different ways, and generally, people don't really want to scratch the surface because you can get into some really dark territory real fast.
Related Authors: Robert Crumb Jhonen Vasquez Rube Goldberg Harvey Pekar Joe Shuster Robert Kirkman Todd McFarlane