Famously, the biggest contribution the series made to Batman lore was the creation of Harley Quinn. The Joker's psychotic girlfriend is set to make her big-screen debut in next year's Suicide Squad, but her first appearance anywhere in the Batman canon was as a minor role in BTAS episode Joker's Favor, before she became a fan-favourite and her role was expanded. Of all of the show's Harley-centric episodes, however, we've plumped for the one that tells just how she fell for her puddin', the Joker. Dr Harleen Quinzel was once the Joker's psychiatrist at Arkham before she became smitten with her patient and broke him out of the hospital - and joined him on his life of crime, now going by the name of Harley Quinn. As well as showing Harley's origins, this is also perhaps the best episode for demonstrating the tragedy of Harley being in an abusive relationship with the Joker from which she can never escape. See, we told you this show wasn't just for kids.
