Edward Nigma ran away from his dismissive father at a young age to join a carnival. During the carnival, he began to do crimes, leaving behind riddles and puzzles for his enemies to prove their intelligence. Eventually he settled in Gotham due to Batman outsmarting him, and refuses to leave until he can prove his superiority to him. Despite this, Batman's knowledge of extremely useless trivia never fails to come in handy for The Riddler's puzzles. That, and also people looking up the answers.