"You won’t kill me out of some misplaced sense of self-righteousness. And I won’t kill you, because you’re just too much fun. I think you and I are destined to do this forever."
―The Joker to Batman.
In The Dark Knight, The Joker is depicted as a maniacal criminal mastermind who terrorizes Gotham City and whose goal is to plunge it into anarchy. The Joker has been described as a “psychopathic, mass murdering, schizophrenic clown with zero empathy.” He was portrayed by the late Heath Ledger, in the role that won him a posthumous Academy Award for Best Supporting Actor.
"Some men aren’t looking for anything logical, like money. They can’t be bought, bullied, reasoned, or negotiated with. Some men just want to watch the world burn."
―Alfred talking to Bruce Wayne about how the Joker is different from most criminals.
The Joker claimed to not be insane, but rather just “ahead of the curve”. This may have been legitimately true, in the sense that he seems to subscribe to a more morally nihilistic mindset, yet he still exhibited many symptoms of various failings of mental health. The Joker was described as having “zero empathy”, which is shown throughout as being true. (This led him also to doubt how deep human morality really runs, as he once said, “These people. When the chips are down; when everything has gone completely to hell, they’ll eat each other”.) When Batman is throwing the Joker around the room and attacking him, demanding for the location of Rachel and Harvey, he takes the assault with pleasure as he laughed while being beaten by the Batman.
Similarly, when one of his minions got electrocuted in his attempt at removing Batman’s mask, he proceeded to laugh hysterically, kick the minion, then mocked him by making noises similar to that of someone being electrocuted, before spitting on him and resorting to his attempt at removing the mask himself. Along with being extremely sadistic, the Joker seems to have very little care for his own safety, such as when he was telling Batman to run him over with his Batpod, and when Batman threw him off a skyscraper building to his supposed death and he did nothing but laugh (only for Batman to save him with his grapple gun), although both could have also been due to the Joker believing that either Batman would not directly murder him or that he would still ‘win’ by provoking Batman into proving him right by forcing the Dark Knight to commit murder. Similarly, when Gambol attempts to have the Joker killed during a mob meeting, the Joker also revealed that he wired himself with explosives, having anticipated the possibility that he’d be gunned down during his meeting.
The most notable example in his utter lack of self-preservation, is when in the hospital, he gives Harvey Dent, after disfiguring him, and killing his girlfriend Rachel, a gun, and forcibly points it at his head, gambling his life on the chance that Dent would adopt his philosophy of anarchy. Though, subtly, he kept his finger in front of the hammer of the gun, which would keep it from firing.
He exhibits various symptoms of an antisocial personality, blatantly disregarding laws and social norms far beyond standard deviant behavior. The Joker also has a low level of inhibition and a relentless drive to disturb the status quo. He is driven by something other than money: he complains that the criminals of the mob are just seeking a profit and that the city deserves “a better class of criminal”, namely himself.
While The Joker does attempt to take control of the city, recruits mob henchmen, he appears to hold his philosophy of chaos higher than himself. He describes himself as merely an “agent” of chaos (in his speech to convince Harvey Dent to let go of his beliefs so he could prove in his ultimate plan that even the most noble of men can sink down to the Joker’s level).
He also doesn’t actually care about money, as evidenced by his burning of the mob’s money that he earned to recover Lau in front of the Chechen and stating that his actions aren’t “about money.” However, he did see some usefulness of money, as evidenced by the implication that he used the money he stole from Gotham National Bank to create his custom suit, acquire his equipment and weaponry, and hire others to form his own gang as the mob’s agents were simply used as a means by Joker to gain control of Gotham’s infrastructure and cripple the mobs power.