The Joker - Batman: Shadow of the Bat #37
Batman: Shadow of the Bat #37 focuses on a man named Wilde Norton who, in the name of revenge for his family's murder, is actively hunting The Joker. Norton's hate turns to obsession when he receives The Joker's medical records from Jeremiah Arkham. This is important, though, because his obsession with reading the medical records gives the reader a lot of insight into the mind of The Joker.
The origin story in Shadow of the Bat syncs up perfectly with the story of The Killing Joke but takes our level of psychological analysis a few steps further through the inclusion of medial tests and quotations.
The events of the story follow The Joker's goons as they kidnap random citizens for some maniacal deed. One thug, Pete, is captured by the Police. Norton hears about this and goes to question Pete. When he reveals The Joker's location (Mercey Mansion) Norton kills him and takes off.
"In my dream the world had suffered a terrible disaster. A black haze shut out the sun and the darkness was alive with the moans and screams of wounded people. Suddenly a small light glowed. A candle flickered into life, symbol of hope for millions. A single tiny candle, shining in the ugly dark. I laughed, and blew it out." - The Joker
While this story does not feature The Joker as a prominent character it is, almost entirely, about him. The inclusions of medical records and psychiatric files give a lot of insight into the mind of the Clown Prince of Crime and make this book a necessary read for Joker fans.