Edward Nygma, better known as the Riddler, is a major antagonist in the DC Universe, specifically serving as a major antagonist in the Batman franchise.
He is a genius criminal mastermind who is obsessed with riddles and always leaves complex clues for the ones trying to solve his crimes. Unlike Batman's other villains, in most interpretations, the Riddler is primarily driven by an extreme obsession with proving he is smarter than Batman and continuously tries to create puzzles and riddles that even he cannot solve.
The Riddler is also one of the few people that managed to discover Batman's true identity of Bruce Wayne (although this knowledge was presumably lost following the New 52). He is specifically the overarching antagonist of Batman: Hush, the main antagonist and Batman: Zero Year and one of the main antagonists of The War of Jokes and Riddles arc in the Batman: Rebirth comics.