Zero Mostel (1915-1977) was an American comedian, actor and singer whose credits ranged from Tevye in the original Broadway version of Fiddler on the Roof to Max Bialystock in Mel Brooks' The Producers.
He died on September 8, 1977, days before his Muppet Show episode aired (Episode 202). In previous years, he appeared in inserts on Sesame Street, in photographs in the 1974 book Sesame Street Book of Opposites and provided the voice of the evil Spellbinder on The Electric Company.
(Commenting on Jim Henson's Muppets): "He has the best possible actors. If you have a disagreement with them, you can always use them to wash your car."