Oppenheimer took over as Rudy starting with the second pilot film, Wine, Women and War, up until the introduction of The Bionic Woman in 1975, whereupon Martin E. Brooks took over as Wells up until cancellation.

He appeared in the Star Trek: The Next Generation episode "Rightful Heir" as a Klingon cleric, Koroth, a primary instigator of the cloning of Kahless, on Deep Space Nine as a Starfleet Captain Declan Keogh in command of the USS Odyssey and as an alien ambassador in Voyager.

Oppenheimer also appeared as film director Cecil B. DeMille in the 1994 Broadway production of Andrew Lloyd Webber's Sunset Blvd.

[3] Other notable voice roles include Thundarr the Barbarian, Vanity on The Smurfs, Rhinokey and Crock from The Wuzzles and Falkor, Gmork, Rockbiter, and the Narrator from 1984's The NeverEnding Story.

He was the voice of the never-seen Alistair Crane on the soap opera Passions until 2004, when the character was finally shown on camera, played by David Bailey.

He additionally voiced Harold in Fallout: Brotherhood of Steel, Dyntos and the Chariot Master in Kid Icarus: Uprising, and Darm and the Narrator in Ys.