[AlexanderHowl]

I like to think that Joker is a malevolent spirit that possesses one victim at a time, driving them insane, which is why 'he' can never truly die, how 'he' escapes prison so easily, and why 'he' always has a different back story. When possessing a new victim, 'he' retains their memories and skills and takes on aspects of their previous personality. When needed, 'he' commits suicide and take a new body, justifying Batman's avoidance of killing 'him', as the only way to trap 'him' is to keep 'his' host alive.

In truth, 'he' has likely existed forever in the region that would become Gotham, but 'he' would have been trapped for millennia by the magic of Lenni Lenape shamans before the European invaders unwittingly set him free during the 17th century by slaughtering the people who imprisoned him. The Joker persona is only the most recent persona of the spirit and a number of horrific crimes over the past few centuries can probably be linked to 'his' various personas. 'He' feeds on pain and suffering and, until permanently destroyed, 'he' will always plague Gotham, though 'he' is not bound to it.