The Two-Headed Monster is a comical, light purple monster on the show. It has two heads that speak with a heavy accent and sometimes talk as if they're speaking another language, though it may just be gibberish. Their primary role is to demonstrate opposites. In recent seasons they "assist" Big Bird in his search for Ernie during their hide and seek game called "Journey to Ernie". The heads generally discuss amongst themselves, and each of the monsters' arms point in a different direction. Then, the heads often debate and the arms switch directions as they say "that way," and then swap back again. Created when a writer noticed Jerry Nelson and Richard Hunt, the character's original performers, were goofing off imitating a monster with two heads, which led to the design of the character.

In The How Many Game, hosted by Guy Smiley, it was said that their names were Frank & Stein. Sesame Workshop itself does not generally acknowledge this as part of canon. The two sang "Hi De Ho Man" with guest star Cab Calloway.