The Joker is a supervillain, Gotham's most notorious criminal and the archenemy of Batman. He is voiced by Mark Hamill.
Jack Napier was a lab technician who was down on his luck. After his failed career as a comedian, he was unable to support his pregnant wife Jeannie and had no choice but to turn to crime. Jeannie later died due to a malfunctioning water heater. Under the guise of the Red Hood, he and the Valestra mob planned to rob a chemical plant. Unfortunately, Batman attacked and Napier fell into a chemical vat, changing his appearance into that of a deranged clown. Driven insane by his new look, Napier called himself the Joker and has been terrorizing Gotham City ever since.
The Joker was originally a lab technician and later comedian 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.
Former lab technician (when he was still Jack Napier)