Sam Rockwell was among a shortlist of actors considered for The Joker in Christopher Nolan's The Dark Knight, and of course, the role eventually went to the late Heath Ledger. Would It Have Worked?: Probably, but not certainly. Rockwell is an excellent actor, though he didn't have masses of experience playing the villain by 2008, and even since, his part as Justin Hammer in Iron Man 2 wasn't a great part (by no fault of his own). Rockwell's piercing eyes and (potentially) evil grimace would no doubt make him have the look of The Joker down pat: it's just a question of whether he could go to the dark places needed to make the Nolan version work. Still, this is exactly what people said about Ledger prior to the movie's release, so for Rockwell, the balance of probabilities says "yes".