Joker Appearances
The Joker is is the long-time arch-nemesis of DC Comics Batman, one of the most successful comic book characters in the world. Widely recognized as one of the best villains in popular culture; the Joker is practically a jungian archetype at this point. His every appearance is wildly different than the last, but is still immediately recognizeable as the same character.
The Joker was actually the brainchild of the long unrecognized co-creator of Batman Bill Finger, who based him on Conrad Veidt's character from the 1928 silent film The Man Who Laughs.
A few early serials aside, the first truly memorable live-action Joker was Cesar Romero in the classically campy 1960's Batman series. He famously didn't want to shave off his mustache, so it's actually painted over with the rest of his face.
For an entire generation, Jack Nickolson's portrayal of the Joker in Tim Burton's 1989 smash blockbuster Batman was the definitive version...
... although he was certainly given a run for his money by the Joker from Batman: The Animated Series. Voiced by Mark Hamill in one of the most famous voice performances ever, this is often sited as the single most influential take on the character, and has carried over into several other media including the iconic series of Batman: Arkham console games.
Jared Leto appeared as a very divisive version of the Joker in the 2016 movie Suicide Squad, Leto fameously did a lot of weird method acting for this performance, but most of his work wound up cut from the film, making him just a weird side character that wasn't really worth the build-up.
The 2019 movie Joker, a stand-alone origin story for a character that doesn't really NEED an origin, is a pretty problematic movie for a lot of reasons, but it's hard to deny that Joaquin Phoenix's take on the character is really good...
... But all that said, there really is no doubt just which Joker is being portrayed in GND. Heath Ledger's Joker from the 2008 film The Dark Knight is completely unique among all the various versions of the Joker that have made it to the screen. It's not only one of the best takes on the Joker, it's among the top ten or fifteen characters ever created in a movie EVER, Rip, Heath.
Comic Appearances
GND Commish: Bday Psychos - In an out-of continuity comic, the building throws a b-day party for Byaghro. In attendance are Sarah, Jareth, Christine, James, Sweeney, Random Chickens, and visitors Will Turner & The Joker.
GND 124 - Sarah & Christine pass Legolas on their way out the door and chat with Shilo about her status with her boyfriend, her dad, and her boyfriend's ex...only briefly mentioning Jareth's peaches. meanwhile Nick & Danny have Graverobber in lock-up, along with Alice Cullen & the Joker.