It's not the Joker, but the Trickster! Mark Hamill will reprise his role from the '90s Flash series for the CW's The Flash in one episode next year.
Hamill originally played The Trickster in the '90s Flash series and the animated series Justice League Unlimited. This will be his first time in two decades playing The Trickster in a live-action format.
"Having Mark reprise his role as The Trickster was on our original wish list when we were planning our version of The Flash. Christmas and Chanukah came early for us this year when he said yes! We are beyond humbled and excited to have him joining us for another round of deadly trickery!"
CW noted this Trickster will be a new interpretation of the character. According to HitFix, the CW stated:
Mark Hamill returns in a brand new interpretation of James Jesse (aka The Trickster), a role he originated on the 90's "Flash" series. In this new iteration, The Trickster is an anarchist terrorist con man serving a life sentence in Iron Heights who helps Barry (Grant Gustin) and Det. West (Jesse L. Martin) to foil the city-wide attacks of a wannabe Trickster eagerly following in the original's deadly footsteps. The episode will reunite him with John Wesley Shipp who went up against him as the original "Flash" on the CBS version.
Hamill's Trickster will appear in the 17th episode of The Flash, due to release sometime in 2015.