Skeletor

Skeletor is the main antagonist of the media franchise, Masters Of The Universe. He is an archenemy of He-Man. Skeletor is 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(later revealed to have led to Etheria) 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 the whole universe.

Filmation Series
In the original series, Skeletor is the main villain, either appearing in the flesh, or acting thru one of his minions, such as Evil-Lyn or Whiplash. Due to the semi-comedic nature of the show, Skeletor is shown to be arrogant, whiney, childish, and incompetent. Examples of his immature behavior is when he attempted to hijack a circus simply because the owner refused to perform at Snake Mountain, throwing a tantrum at his henchmen's stupidity, and repeating that he isn't a nice man. In one of the post-series minicomics, it's hinted that Skeletor is He-Man's uncle, Prince Keldor.

the New Adventures of He-Man
In the controversial semi-sequel series, Skeletor is still the main villain, but is presented as being more mature and villainous than in the Filmation series, and has a very morbid sense of humor, often spouting out one liners and jokes ala Gene Hackman's portrayal of Lex Luthor. In this series, Skeletor follows He-Man to the world of Primus and joins forces with the Mutants, pretending to follow the orders of the idiotic Flogg, while manipulating him all the way. In episode six, Skeletor is transformed into a more powerful version of himself via an evil crystal and stays that way until the final episode. In episode sixty-five, Skeletor is finally defeated when He-Man sends him and his lover Crita rocketing thru space. In the final scene, Skeletor vows that he'll return and gives out a chilling laugh.

Live Action Film
Skeletor also appeared in the live action film Masters Of The Universe and was obsessed with becoming a god via stealing the Key Of The Universe - however his plans were opposed by He-Man and his group, who went as far as opening a portal to Earth in order to evade him: Skeletor wasn't so easily shaken however as he sent several henchmen after them (most of them well-known He-Man villains such as Beast-Man). When his servants failed him Skeletor arrived on Earth himself via a huge floating throne, accompanied by an entire army and forced He-Men into becoming his slave with the threat of killing his friends should he resist.

Skeletor then took the Key Of The Universe and with it became a god, transforming into a golden vaguely Aztec-inspired super-being as a result - however He-Man's friends managed to come to his aid and when Skeletor ordered his men to kill them He-Man became enraged and the two enemies engaged in a climatic battle, although he put up a good fight Skeletor wasn't a match for He-Man and ultimately lost the battle: transforming back to his usual form after his godlike energy was dispersed.

He-Man attempted to show mercy to his old for by informing him that the battle was over but Skeletor replied with a taunting "yes.. for you!" before attempting to kill He-Man again, only to plunge to his death down a pit in a similiar manner to the Emperor in Return Of The Jedi. Only for him to live and come out of the water and say " I'll be back!"