The Riddler, also known as Edward Nigma, is a fictional character, a comic book supervillain published by DC Comics, and an enemy of Batman. Created by Bill Finger and Dick Sprang, the character first appeared in Detective Comics #140 (1948).
Riddler is part of The Legion of Doom in "It Takes a Village Idiot, and I Married One" when Lois Griffin exposes their plot to sell yellow-cake uranium to Adolf Hitler. However, he does not appear in the episode.
When Peter Griffin is worried that Patrick Pewterschmidt may have committed another murder in "Killer Queen", he threatens to do to him when he did to the Riddler. A cutaway shows a Batman-style fight with colorful verbs describing the action.