When Batman returns a severely injured Joker to Arkham, she dons a jester costume to become Harley Quinn, the Joker's sidekick. The Joker frequently insults.
Dr. Harleen Frances Quinzel, also known as Harley Quinn (a pun on the word 'harlequin'), first appeared in the Batman: The Animated Series episode 'Joker's.
One night, after the Joker's most recent escape and re-capture by Batman, Quinzel snapped and resolved to free her beloved Joker and run off with him, adopted.