Reiner has had a long on-camera career, including guest roles on the long-running German TV series Tatort, Derrick, and Der Alte. In Mario Bava's 1964 horror thriller Blood and Black Lace, Reiner played Inspector Sylvester (dubbed in the English version by Paul Frees).
As a voice actor in his own right, Reiner has lent his slightly nasal, authoritative tones to Vincent Price in three films, Geoffrey Bayldon in Casino Royale, Paul Benedict in The Addams Family, Peter Sellers in The Magic Christian, Harry Secombe in Oliver!, and Wylie Watson as Mr. Memory in The 39 Steps.
TV dub roles include Hayden Rorke as Dr. Bellows on I Dream of Jeannie, Philip Jackson on Robin of Sherwood, and guest stars on The Incredible Hulk. In animation, Reiner voiced the donkey in the 1969 German animated satire Die Konferenz der Tiere, as well as dubbing Duke Igthorn on Disney's Adventures of the Gummi Bears, Grimsby in Disney's The Little Mermaid, Professor Farnsworth on Futurama, J. Jonah Jameson on the 1980s Spider-Man, and a variety of roles in the Asterix films (including stuffy Britishers, Julius Caesar, and Getafix the druid).