While researching the lunatics at Arkham Asylum, a young psychiatric intern named Harleen Quinzel met the Joker. She fell instantly in love with him. After helping him escape from the asylum more than once, Harleen was suspected by the authorities who revoked her license and placed her in her own cell. During an earthquake in Gotham City, she fled and became Harley Quinn, the sidekick to the Clown Prince of Crime himself, the Joker.
She frequently refers to The Joker as "puddin" and "Mr. J".
One time, the Joker tired of Harley, and he sent her off on a rocket. She crash landed in a park in Gotham and was nursed back to health by Poison Ivy. Those two led a few capers themselves. The Joker and Harley made up afterwards.
She also has her own monthly DC Comics comic book series entitled Harley Quinn.
A version of the character, played by Mia Sara, also appeared in the television series Birds of Prey.
Comic book fanatic and film-maker Kevin Smith named his daughter Harley Quinn.