Which muppet was NOT in the first season of "Sesame Street"?

By the time Elmo showed up in 1980, Big Bird, Oscar the Grouch, and Cookie Monster had already established themselves as "Sesame Street" royalty. He was originally a nameless background muppet until Kevin Clash got his hands on him (literally). Clash decided Elmo should be sweet and loving rather than another generic monster, a personality shift that turned him into the breakout star. He went on to get his own segment and became one of the most recognizable children's characters in the world. And the timing worked because "Sesame Street" needed fresh energy to compete with flashier kids' shows in the 1980s, and Elmo's enthusiastic personality and high-pitched giggle gave the series the boost it needed to stay relevant for a new generation of viewers.