Grump's earliest known appearance was as a character living in a shabby house in a commercial for the Federal Housing Administration in the 1960s. He also performed the "Visual Thinking" sketch on The Ed Sullivan Show (where he was voiced by Jerry Juhl) with a pre-Kermit the Frog in 1966. He also appeared in a few scenes in The Muppets on Puppets.
By 1969, he was used as the Head of the Board in the Sesame Street Pitch Reel (where he was performed by Jim Henson), and later reworked for Sesame Street's first season as a hippie, and The Muppet Show as Mary Louise.
Grump was rebuilt for the Muppet Meeting Films, where he was paired with Leo as the two principal players. Grump, in keeping with his name, was bitter, constantly grousing, and never entirely sure of what was going on. He assisted Leo in various presentations, often to his regret.