The Riddler is obsessed with riddles, puzzles and word games. He delights in forewarning both Batman and the police of his capers by sending them complex clues. The character is often depicted as wearing a domino mask either with a green suit and bowler hat, or a green jumpsuit. His trademark is a green "?".

The Riddler is typically portrayed as a smooth-talking, yet quirky, victim of an intense obsessive compulsion. This was first introduced in the 1965 issue of Batman (titled, "The Remarkable Ruse of The Riddler") in which he tries to refrain from leaving a riddle, but fails. This compulsion has been a recurring theme, as shown in a 1999 issue of Gotham Adventures, in which he tried to commit a crime without leaving a riddle, but fails: "You don't understand. .. I really didn't want to leave you any clues. I really planned never to go back to Arkham Asylum. But I left you a clue anyway. So I... I have to go back there. Because I might need help. I... I might actually be crazy."

The Riddler was popularized by Frank Gorshin’s over-the-top, Emmy-nominated portrayal in the 1960s Batman television series. Jim Carrey played the Riddler in the 1995 film Batman Forever with Gorshin as his inspiration. The character was also featured in Batman: The Animated Series and The Batman.