Nolan has said explicitly that Alan Moore's quintessential dissection of the Joker, 1988's one-shot "The Killing Joke," was an inspiration for his take on the character in "The Dark Knight." There was an even darker, heightened sense of danger around the character in those pages, but more than that, the story is very much about what it takes to break good men. That is the ultimate thesis of the film, which presents a quartet of characters -- Batman, Gordon, Harvey Dent and the Joker -- with their own ideas of how the world should work, their own impositions as such, and their own lessons learned as a result. Perhaps it wasn't as narratively connected as other tales, but the thematic residue is unmistakable.