Mr. Dragon
From Muppet Wiki
Mr. Dragon is a fierce dragon terrorizing an imaginary countryside in the Sesame Street song "Imagine That." Ernie imagines being a brave knight who scares the dragon away by shouting, "Mr. Dragon, you'd better behave!"
Mr. Dragon also appeared in in A New Baby in My House (where Prince Firstly opts to name him Spot) and the "Books" episode of Elmo's World.
