Mark Hamill is almost as famous for being the voice of The Joker as he is for playing Luke Skywalker. In this Justice League Action short from Cartoon Network, Hamill does all the voices: the Joker, Trickster, and "famous actor Mark Hamill," which is a younger and somewhat steroid-enhanced version of Hamill -as you would expect in a comic book character.
The plot proves to be weirdly meta when "famous actor Mark Hamill" saves the day by using his unique superpower- his voice acting skills! -via Laughing Squid