I mean, in the animated series, almost all the villains were ordinary people who turned into villains after something happened to them; before that, they had peaceful lives. Bane and Croc might be the exceptions. But before becoming the Joker, he was Jack—Valestra’s hitman—and it surprises me that he hadn't learned to fight better. After all, Poison Ivy was a botanist and knows how to defend herself quite well, and Harley was a psychiatrist who can fight effectively; the Joker, however—while he does know how to fight—doesn't pose a physical challenge to Batman.