3. Batman: A Killing Joke
Very little of this plot in this story found its way into the films, but it is important nonetheless. Penned by superstar Alan Moore (Watchmen, V for Vendetta), this book delved into the Joker's master plot to break Batman's spirit by attacking those closest to him. The specific elements of the plan bear very little similarity to the elements used in The Dark Knight, but this was one of the first tales to truly explore the Joker's psychosis, and was key to understanding Heath Ledger's portrayal of the Clown Prince of Crime.