In cities across Europe and America, tales have been told of an affable 'Laughing Butcher' who, with a joke and a smile, would lead unsuspecting street dwellers to their deaths - feeding them to his 'pets,' hordes of rats that lived beneath his shop. The police never investigated these tales, but when the Butcher moved to Gotham, the Batman discovered his shop and attempted to bring him to justice. The Butcher fled to a nearby tannery where he fell into a vat of chemicals. These chemicals bleached his skin white and distorted his face into a rictus grin. No longer able to hide in the shadows, the Butcher began calling himself 'The Joker' and set about committing more audacious and horrific crimes, all aimed at keeping his pets well fed.
Gaslight Joker typically acts as if he were performing for an audience, which in his warped mind, are his pet rats. To that end, his movements and attacks are both brutal and flamboyant.