Answer: Tim Curry
During the casting of the 1989 live action Batman film, Tim Curry was considered for the role of The Joker. While the role in the live action film went to Jack Nicholson (a role for which he received hugely rave reviews), Curry got his chance to play The Joker again in 1
Curry was the original voice of The Joker in Batman: The Animated Series but after recording the first episodes and testing the screen with audience, Curry was cut out of the cast. The reason? His rendition of The Joker was extremely disturbing for the children in the audience. His outspoken voice and intensity were perhaps a bit too much for even the exaggerated Joker character.
Batman: The Animated Series was perhaps dark, grainy and attractive for an animation series for children. But at the end of the day it was still a show for children and immediately scaring the target audience was bad for business. Curry was replaced by Mark Hamill, who went on to broadcast the rest of the series The Joker, as well as in several Batman animation films and video games.