The Joker is a supervillain, Gotham's most notorious criminal and the archenemy of Batman. He is voiced by Mark Hamill.
The Joker was originally an unidentifiable criminal with a checkered past, who started out as both a hitman and a chauffeur working for the Valestra mob. One of his final tasks was to murder Carl Beaumont.
Returning to Gotham City, the thug formed his own gang and staged a robbery at the Ace Chemical Plant, which was thwarted by Batman. Either because Batman pushed him, or he stumbled after getting punched, the thug fell off a catwalk and into a drainage vat of chemical waste that washed him out into the river, changing his life forever. The chemicals had an adverse effect on him: they dyed his hair green, his skin was bleached white, and his lips were permanently stained red. Vowing to show the world the triumph of his comic genius, the career of one of history's most dangerous and intelligent psychopaths, the "Joker", began.
Taking the alias of the "Joker", he continues to cause mayhem at Gotham City, enjoyed torturing Batman and was acquainted with Harley Quinn numerous times.