A voice actor is an actor who only provides voice talent and does not appear on-screen. Voice actors are most commonly used in animated television programs, but are also used in video games as well as shows that feature puppetry, claymation or marionation. One of the most well-known voice actors in television is John Kassir, who provided the unmistakable voice of the Crypt Keeper in the HBO horror anthology series Tales from the Crypt. Another voice actor of reputable note is Peter Cullen, best known for providing the voice of heroic autobot leader Optimus Prime in the Transformers cartoon franchise as well as the live-action feature films.