Think of some of the great nemesis pairs in fiction: Harry Potter and Voldemort, Katniss Everdeen and President Snow, Professor Xavier and Magneto, Superman and Lex Luthor… But there's none better than Batman and The Joker.
The Joker is responsible for numerous tragedies in Batman's life like paralyzing Batgirl and murdering Robin. He's such a popular character that he's ranked 8th on the list of Greatest Comic Book Characters of All Time. One reason he's the perfect nemesis is The Joker is the complete and utter opposite of Batman: he's savage, violent, unpredictable, and will do anything because he has no respect for human life. As Michael Caine said in Dark Knight, The Joker "just wants to see the world burn."