In Grant Morrison's run of Batman and Robin, easily one of the more unique Batman villains to arrive was the ironically named White Knight.
The White Knight seemed to want to cleanse the people of Gotham, but very specific ones. Mainly, the relatives of Arkham inmates. It is revealed that he was once a victim of the villain Phosphorous, and sought revenge by killing anyone related to anyone at Arkham. The White Knight proved a might foe for then Batman Dick Grayson, but eventually, he was put in Arkham himself...much to his delight.