Joker is a tall, thin gentleman of indeterminable age. His forensic history is extensive, having committed more than 2,000 murders (Dixon and Nolan, 1996); several of these comprise many notable members of Gotham City's elite. read more
Specifically, I believe that the Joker is a classic example of antisocial personality disorder, while Harley fits the bill for histrionic personality disorder. Symptoms of personality disorders can be found in the DSM-V, the book that details all mental illnesses. read more