In addition to performing a variety of characters, Oz was one of the primary collaborators responsible for the development of the Muppets. Oz performed as a Muppet performer in over 75 productions, including "Labyrinth", video releases, and television specials, as well as countless other public appearances, episodes of "Sesame Street", and other Jim Henson series. His puppetry work spans from 1963 to the present, although he semi-retired from performing his Muppets characters in 2001. In 2001, his characters were taken over primarily by Eric Jacobson (with David Rudman as Cookie Monster).