Batman: The Animated Series introduced a generation of fans to the Caped Crusader, but it also made longtime DC aficionados familiar with one feisty villainess. Harley Quinn is now a popular character in her own right, but she started out as The Joker's sidekick in the cartoon. Voiced by Arleen Sorkin, Harley has gone on to become a major DC icon
Source:https://www.cbr.com/arleen-sorkin-harley-quinn-creation/