A major theme in this graphic novel is that Batman the main protagonist and The Joker the main antagonist are a mirror of each other. They both have had traumatizing moments in their life that had driven them mad but they each reacted in a different way. Batman reacted to his parents murder by trying to stop needless crime and violence and stopping at nothing to do so. The Joker reacted to his wife's death and him falling into the polluted water by becoming completely mad. After the incidents he began to see the world in nihilistic views, and began to not care about life, he believed that everyone's life could be ruined with just one bad day, and his goal was to show that to everyone that would listen; and if they didn't listen he’d make them
