Skeletor is the main antagonist of the media franchise Masters of The Universe. He is He-Man's archenemy. Skeletor is also called the "Evil Lord of Destruction", and his threat is to rule all of Eternia. Skeletor is a former pupil of Hordak, leader of The Evil Horde.
When Hordak and his Horde invaded Eternia and stormed the palace, Hordak broke in and kidnapped one of the King and Queen's twin babies. Man-At-Arms and the Royal Guard captured Hordak's apprentice Skeletor and forced him to divulge the whereabouts of his master. Hordak had retreated to his base of operations Snake Mountain.
When cornered, Hordak opened up a random dimensional portal and leaped through with the baby Princess Adora still in his possession. Skeletor remained on Eternia and raised an army of powerful minions of his own and took over as ruler of Snake Mountain. Skeletor's main goal is to conquer the mysterious fortress of Castle Grayskull, from which He-Man draws his powers. If he succeeds, Skeletor would be able to conquer not only Eternia, but also the entire universe.
In the new continuity of the 2002 animated series, Skeletor is confirmed to be Keldor, his appearance as such is shown and his exploits partially depicted. However it is not mentioned in this continuity that he and Randor are brothers, and he is seen to have Skeletor's blue skin and some other slightly nonhuman features whilst still Keldor. In a he-man.org interview with one of producers of the 2002 series, it is revealed that Keldor is indeed the paternal half brother of Randor; Keldor's differing appearance was due to the fact that he and Randor had different mothers. While Randor's dad and Keldor's dad are the same man, Randor's mom and Keldor's mom were different women.
In the Legacy of Chris Thorndyke,
And he is reprised by Mark Hamill in the English dub and will be voiced by Takehito Koyasu in the Japanese dub.