Skeletor is a dark sorcerer from Eternia. A sinister humanoid figure with blue skin and usually dressed in a hooded attire, he earns his name from his bare-bone face which resembles an animate Human skull. He is also a former member of the powerful multi-species affiliation known as the Evil Horde, but left the organization after betraying his master Hordak in a mission to kidnap Princess Adora of Eternia. After that, Skeletor has assembled his own group of loyal and not-so-loyal followers to attempt to conquer Castle Grayskull and the secrets to the infinite power source it possesses for being located in the exact center of the universe. However, his plans have been repeatedly foiled by He-Man and the other Heroic Warriors.
Skeletor is the tyrannical ruler of the dark side of Eternia, operating from his lair on Snake Mountain. He prides in his evilness and his perceived astuteness, and is usually ambitious but optimistic about his plans. He shows little tolerance towards failure and incompetence and usually gets mad at his minions when something goes wrong. A student of the occult; he has mastery over magical powers and his knowledge has only increased after being tutored by Hordak. He carries around a magical weapon known as the Havoc Staff to perform his spells, and is capable of teleporting at will. Besides his advanced magic, he has also displayed technological knowledge which allows him to build various machines and contraptions; and is skilled at physical combat as well. He has a pet Dylinx named Panthor.
Although Skeletor's origins are secret to most people, he was actually born as a half-Gar warrior and sorcerer named Keldor, who lost his face in an accident when he attempted to attack his half-brother Randor with acid; only to have the acid splash on the future-king's shield and hit Keldor instead. To save the life of his student, Hordak then merged Keldor with an extra-dimensional demon, thus creating Skeletor.
- In the original concept for the series, Skeletor was the evil ruler of a planet called Infinita, located in the same orbit as Eternia. It was only the 2002 series that confirmed his identity as Keldor, which, tying into earlier portrayals of Keldor as King Randor's brother, makes Skeletor none other than the uncle of his arch-nemesis He-Man. This was later fully confirmed by his Masters of the Universe Classics biography.
- The name Infinita has been used to refer to an alien dimension that Trap Jaw hails from.
- Despite the portrayal of how Keldor lost his face to acid in the 2002 series; other iterations of the franchise make it look like Skeletor isn't actually disfigured and the skull is just the natural look of his face. This is especially visible in the live action movie, in which it is clear that he is simply an alien whose face resembles a skull, rather than having an actual skull for a face. In The New Adventures of He-Man, his bright red eyes are clearly visible, and also give him a more alien look.