Jack Napier was abused as a child. His father would beat him and his mother ran away. He eventually killed his father and became a mugger. One of his crimes included the murder of Thomas and Martha Wayne. Years later he was married and he tried to be a comedian. He failed at being a comedian and his wife was killed by loan sharks. Later he adopted the Redhood persona and started his own drug ring. But during an encounter with Batman he fell into a vat of acid. The acid turned his skin white and his hair green. The change drove Jack insane and he became the Joker.