Jim Gordon is a main staple of the Batman Universe, serving as Batman's foremost ally within the Gotham City Police Department. However, over the years "Commissioner Gordon" has had to suffer through some of the darkest lore of any character in DC Comics, having his entire family (and sanity) torn apart by Gotham's violent darkness. Indeed, the focus of DC's The Joker limited series has really been Gordon confronting and taking stock of how much of the darkness he's endured was at the Joker's hands. By the end of James Tyion IV's story, Gordon has decided that he's had enough...
(WARNING: SPOILERS Follow!)
The story arc of The Joker (vol. 2) saw Gordon hired by an emissary of the Court of Owls to hunt down the Clown Prince of Crime. However, that simple mission of vengeance became a Nietzschean descent into a much deeper abyss: Gordon uncovered an entire clandestine criminal network that spans the globe – a network that not only shelters supervillains between their capers, but collected DNA from those same villains to create entire library of next-gen villain clones. It was also revealed that Bane faked his own death and staged Gotham's infamous "A-Day" mass killing at Arkham – as well as launching Gordon's whole mission in order to draw The Network into the light. Bane ultimately recruited his own female clone, Vengeance, as his new partner. In the midst of all this chaos, murder, and mayhem (and a family of cannibals), Gordon ultimately decides killing Joker wouldn't be the end of the greater evil he now sees at work.
Joker #15 puts the ending framework on the series by having Gordon recount his strange adventure to Batman, before making a big declaration:
"I'm entering private practice with Bullock... I'm happy to leave the capes and tights to you and my daughter for a while," Gordon tells Batman in a classic rooftop conversation. "Just do me a favor and don't let that damn clown stay free for long."
Harvey Bullock took over for Jim Gordon as GCPD commissioner went Gordon went missing for a time; he recently retired from the force during The Joker War event, due to a deep disagreement with the way Gotham City's mayor chose to police the populace. Now these two beloved cops of Batman lore are striking out on their own as private detectives, looking every bit like a new Sam and Twitch from Spawn. A Gordon and Bullock P.I. series is already a win in our book...
The Joker series is on sale at DC Comics.