The clown prince of crime
A failed comedian forced into a life of crime to support his pregnant wife, The Joker pursued Batman disguised as Red Hood. When thwarted by Batman he leapt into a vat of chemicals, turning his skin white, his hair green, and his lips bright red. This disfigurement combined with the loss of his wife drives him insane, and this is how The Joker was born. Or, at least, it's one of the tales he tells about his past. No one is really sure which version is true, and that's just the way The Joker likes it.