From Muppet Wiki

Characters and alter-egos assumed by Cookie Monster in Muppet productions.

Picture	Role	Production	Notes
	Ernie	Sesame Street episode 0158	Bert says that he's seen Ernie eating cookies. The culprit turns out to be Cookie Monster, disguised with Ernie's hair and shirt.
	The Great Cookie Thief	Sesame Street episode 0276	From 1971
	Little Red Riding Hood	Sesame Street	From Sesame Street News in 1979
	Casey McPhee, the Engineer	Sesame Street	From the ballad of the same name
	Alistair Cookie	Sesame Street	Cookie Monster as Alistair Cookie in "Monsterpiece Theater"
	Little Boy Blue	Big Bird's Mother Goose
	Baby Cookie	Sesame Beginnings and The First Time Me Eat Cookie
	A cookie	Sesame Street Halloween card	Cookie Monster dressed as a cookie to go trick-or-treating.