The Two-Headed Monster is a comical, light purple Muppet monster on the television show Sesame Street, first appearing in season 9, 1978.
The right-hand head has purple hair and a black beard, with upturned horns, whereas the left-hand head has black hair and a purple beard, with downturned horns.
They are presumably dicephalic parapagus twins, as their mother made an appearance in one sketch when they sounded the word "mom"; she has a single head and speaks normally.
The creation of this monster was inspired by performers Jerry Nelson and Richard Hunt playing around on the set one day, saying that they were a monster with two heads.
The performers for the Two-Headed Monster are listed in order of the history from the Left Head and the Right Head: The Two-Headed Monster was designed by Jim Henson and built by Caroly Wilcox.