Skeletor, also known as Keldor, is the main villain of the Masters of the Universe franchise. He's He-Man arch-enemy, as well as one of the most iconic villains in cartoons history.
Alan Oppenheimer was the first person to voice Skeletor. He voiced Skeletor, in addition to other characters, in 1983's He-Man and the Masters of the Universe series. He also voiced Skeletor in 1985's He-Man and She-Ra: The Secret of the Sword film, She-Ra: Princess of Power series and the He-Man & She-Ra Christmas special.
Frank Langella was the first (and so far the only) person to play Skeletor in live action. He played Skeletor in 1987's Masters of the Universe film.
Campbell Lane voiced Skeletor in 1990's The New Adventures of He-Man series.
Brian Dobson voiced Skeletor in 2002's He-Man and the Masters of the Universe TV movie and series.
Mark Hamill voiced Skeletor in 2021's Masters of the Universe: Revelation series.