Why I watch Dark Knight a lot.

I've always been intrigued by the super hero ego. How could a person make a life long commitment to saving the lives of other people? What would push someone to do such a thing? Superman is Kryptonian, but poses as human to fit in with the rest of the people he feels the need to protect. Bruce Wayne not only went through a traumatic experience, losing his parents to a mugging, but he is also set for life! I mean, what better way to feel productive in society? You have lots of money, unlimited amount it would seem, and nothing but time to figure out what to do with it. Bruce would never have to call in sick because he doesn't really have a job. All he has is an almost palpable need for immediate justice to those who need it. Let's say you are rich and straight as an arrow. You believe in justice but have the resources to become an iconized vigilante. Would you do it? Why risk your own neck when you could maybe hire someone to do it for you? Cause you would seem like the exact opposite of say, a mob boss? Some of the decisions these super heroes make are a little strange. For example, Why didn't Peter Parker join a sports team? He has the potential to be one of the greatest athletes of all time, but chose a life of crime fighting and being dirt poor. Most of hese guys have a lot in common. One; a traumatic experience shaped them. Two; An incorruptible personality (nobody ever goes "bad"). Three; The will to continue, no matter what, even if it doesn't directly affect them. and Four; they're noble and usually quite modest about their new found "Job".
It would seem this could go both ways... you have super villains and anti-heroes.
The joker, it appears, has an extremely troubled past. a twisted personality. the will to cause chaos. a comfortable sense of homocide. It is the exact opposite of the heroes listed above, but in a way. it is the exact same. the joker is brilliant, but sick. He isn't neccessarily rich, but appears to have unlimited resources in the form of corruption, chaos, murder, and the mutual fellows like him. All of it is rich material for the great stories we all love.