From Muppet Wiki

Leo is a hard-sell business executive who, with his colleague Grump, was a featured player in the Muppet Meeting Films. Leo's enthusiasm, optimism, and general acceptance of the jargon and endless meetings as part of business life contrasted with Grump's grousing. Leo's best known appearance was his solo turn "Sell! Sell! Sell!" , in which a low-key speech becomes increasingly frantic. He served the same function in The Muppet Show pitch reel.

He also appeared on The Muppet Show in episodes 122 and 403 (performed by Steve Whitmire).