Gotham's most notorious criminal, the Joker, proved one of the biggest theories about his madness wrong with a single quote. The Joker's rivalry with Batman is one of the most famous battles in comic history. The two have been fighting for decades with them being complete polar opposites. It's what makes their fights interesting. With Batman's dedication to order and ridding Gotham of crime, Joker is the perfect antithesis of him given how chaotic and evil he is. However, people have been speculating about the Joker's condition for years by questioning if the two would really be enemies if the Joker wasn't driven by madness.
For fans of the Clown Prince of Crime, one of the biggest theories regarding the Joker is that it's his madness that drives the rivalry between him and Batman. Before he fell into the vat of acid in one of his most well-known origin stories, The Killing Joke by Alan Moore and Brian Bolland, he seemed to be a completely different person. No hatred in his heart for anyone. Just a struggling father-to-be trying to provide for his family. This would imply that the Joker wouldn't be who he is if not for his madness, showing that the villain is his warped mind talking and not who he used to be. However, one Batman story shows that this isn't the case at all.
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In the story Batman: Cacophony by Kevin Smith and Walt Flanagan, the Joker is being held in the Arkham Asylum that he helped create with medication that makes him more balanced. This gives Batman an opportunity to talk to the person he believes to be hiding within the Joker in the hopes of helping him escape his Batman obsession. However, when speaking to this medicated Joker, he says one quote
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