The late Arleen Sorkin has a singular honor among superhero actors. Harley Quinn was created especially for her by DCAU guru Paul Dini, famously matching the actor's own personality. It was intended to solve a logistical problem with a single episode (someone needed to jump out of a cake), but it soon took on a life of its own.
Source:https://www.cbr.com/every-harley-quinn-dcau-episode-ranked/