Where Did The Muppets Come From?

This article caught my interest after a coworker let me borrow his DVD of Jim Henson's early work on the Ed Sullivan Show. In it, Cookie Monster is green, has teeth, and doesn't talk. Big Bird is very similar in body but has a tiny head. And Kermit is really the exact same.

I was under the impression that Rolf the Dog was the first official "Muppet", but according to the list, Kermit was around for nearly a decade before Rolf.