Joker (Earth-22)

Joker of Earth is the main antagonist in the history of Batman Who Laughs, he was primarily responsible for the creation of Batman Who Laughs.

History
Joker was the enemy of Batman, and after discovering his real identify, Joker then devised a plan to destroy him, and after killing the remains of Batman's villain's ranks, Joker killed Commissioner Gordon by dissolving acid. And with Batman incapacitated by a paralyzing poison, he then murdered a group of parents in front of their children, thus recreating the scene in which Bruce saw his parents being murdered. With that Joker drove the kids crazy due to Joker Venom. Batman breaks free and kills Joker and kills Joker by breaking his neck, and subsequently becomes Batman Who Laughs and takes the place of Joker.

Trivia

 * Earth-22's, Joker is similar to Injustice's Joker, as both killed people close to their targets, such as Louis Lane for Supperman, and Commissioner Gordon for Batman, both become villains after killing their Jokers.
 * Earth-22 Joker is also similar to Lex Luthor from the Justice Lords universe, both killed people close to their heroes, Batman lost Gordon, while Superman and Flash lost, both were killed by both Batman and Superman, who did become villains in the end.