It seems that in Jonathan Nolan, this rendition of the Joker isn't quite human, but a type of mythical devil of some sort.
http://creativescreenwritingmagazine.blogspot.com/
At around 65% through the interview
"For me the most interesting version of the character is one who was never made at all, just an elemental force. In my imagination, there is no beginning or end to this character, he's kind of always existed. That first frame in Imax, where you see him from behind and he's holding a mask, to me it's as if the moment before that shot he just was conjured out of thin air. Y'know? He's a bit of a devil."
A few moments later, after discussing the Nicholson version (he loved it) and how he feels that giving The Joker a backstory is reductive of the character, he says:
"I think The Joker is and always will be. You see different versions of him in every culture, for thousands of years. Different names, Loki, the trickster, Coyote stories in American traditions." He then says he found it very appealing how in Batman #1 he had no back story, he was "just there."
http://creativescreenwritingmagazine.blogspot.com/
At around 65% through the interview
"For me the most interesting version of the character is one who was never made at all, just an elemental force. In my imagination, there is no beginning or end to this character, he's kind of always existed. That first frame in Imax, where you see him from behind and he's holding a mask, to me it's as if the moment before that shot he just was conjured out of thin air. Y'know? He's a bit of a devil."
A few moments later, after discussing the Nicholson version (he loved it) and how he feels that giving The Joker a backstory is reductive of the character, he says:
"I think The Joker is and always will be. You see different versions of him in every culture, for thousands of years. Different names, Loki, the trickster, Coyote stories in American traditions." He then says he found it very appealing how in Batman #1 he had no back story, he was "just there."