The Joker is a psychopathic criminal from Gotham City. He is the mortal enemy of Batman. Unlike other criminals, who have some kind of goal in mind, the Joker merely wishes to have fun with his shenanigans.
In Downfall Parodies
The Joker portrayed in parodies is typically the Joker in The Dark Knight.
The Joker was also instrumental in Hitler's attempt to kill Justin Bieber. He answered Hitler's advertisement for a killer to destroy the singer, and Dolfy approved him for the job. The Joker chased Bieber throughout Berlin before finally gunning him down.
The Joker is also used as Soalric's main avatar, and his video signature features the Joker heavily.