His identity is a mystery. The only telling of his origin may have been a figment of his twisted imagination. To quote the Joker, "If I'm going to have a past, I prefer it to be multiple choice!" According to the Joker's admittedly faulty memory, he was an out of work greeting cards writer, struggling to make a career as a stand-up comedian. He and his pregnant wife were living a destitute but loving life.
In an attempt to make some fast money before the birth of their child, he made a deal with a couple of members of the Red Hood Gang to help break into a his former employer to rob the safe. The day before the caper was to go down, the future Joker was paid a visit by the police at the bar he frequented. They informed him his wife had died from an electrical short, testing a baby bottle warmer. Distraught and no longer motivated to commit robbery, he attempted to back out, but the gangsters advised him to do so would have dire consequences.
During the robbery, the future Joker was selected to wear the guise of the Red Hood, which was always a random gang member. The three burglars were confronted by a security guard and the Batman. Still wearing his disguise, he ran blindly down the catwalk, falling into the chemical slew. Emerging down river, the water's reflection revealed his face was now bleached white and his hair mottled green. This final misery broke the man's will, transforming him into the homicidal maniac called the Joker.
The Clown Prince of Crime:
The Joker
Other Variations of the Joker:
The Red Hood
Emperor Joker
Gravedigger