Keldor is a character in several versions of the Masters of the Universe franchise. In the 1980s he is only briefly mentioned as being the long-lost brother of King Randor, and in the 2002 animated series he is depicted as Randor's rival who becomes disfigured and becomes Skeletor. It has been generally accepted that these two characters are in fact the same man, although this was never directly stated in any canon until the Masters of the Universe Classics line. As a result of Keldor's introduction to the mythos, Skeletor is unwittingly the uncle of his archnemesis He-Man.
Keldor never appeared in any form of the 1980s Masters of the Universe line, and was only mentioned in one of the final minicomics, The Search for Keldor. In that story, Randor explains that his brother Keldor sought to master the forces of magic, but that he vanished years ago when his experiments backfired, leaving him lost in "dimensions beyond time." Randor and the Sorceress hope to use the power of the Three Towers to peer through the veil between dimensions. When Skeletor learns of this plan, he declares that the secret of Keldor could destroy him, and hastily summons Ninjor, Scare Glow, and Faker (rather than his usual minions) to attack. Skeletor's forces are beaten, but the heroes are prevented from learning anything about Keldor's fate, "except that Skeletor will do anything to stop the search."
In the 2002 Masters of the Universe franchise, the character of Keldor is explicitly the man who becomes Skeletor. In The Beginning Part 1 Keldor leads the Evil Warriors in an assault on the Hall of Wisdom, but Randor and the Masters defend the Council of Elders. When Keldor tries to throw a vial of acid at his enemy, Randor shields himself and the corrosive substance lands on Keldor's face instead. As the Evil Warriors retreat, Randor expresses concern for his foe, but no deeper relationship between the two is revealed on-screen.
A flashback sequence in The Price of Deceit reveals that, following his disfigurement, Keldor recognizes his only chance to survive is for Evil-Lyn to take him to the sanctuary of Hordak, where she summons the ancient villain. Keldor begs Hordak to save his life, no matter the cost; in response, Hordak reduces his head to a disembodied skull hovering over his shoulders. Renamed "Skeletor" by his new master, the former Keldor laughs maniacally at his own reflection. Later, in The Power of Grayskull, Hordak attempts to collect on his debt by demanding Skeletor free him from Despondos, but is ultimately denied.
The biographies printed on the Masters of the Universe Classics toys attempt to reconcile the various backstories of Skeletor/Keldor. Here, Prince Keldor is the brother of Randor in the House of King Miro, although he is also a member of the "rare blue-skinned Gar race." After Keldor is banished from the Royal Palace, he travels Eternia as an outcast until he discovers the ancient spirit of Hordak. As Hordak's apprentice, he learns the dark arts and decides to amass an army to unite all of Eternia under his rule. The evil warriors are defeated by Captain Randor's forces, leaving Keldor near death.
Hordak agrees to save Keldor's life in exchange for his freedom. However, Keldor cannot be trusted to honor a promise to deliver his master from Despondos. Instead, Hordak revives Keldor by merging him with Demo-Man, an evil spirit of Despondos, and in so doing drives his pupil insane. Now known as "Skeletor," he worked madly to open a portal to Despondos in the misguided belief that "his people" dwelled there; this would allow Hordak to free himself. However, Skeletor was defeated by Oo-Larr before any such portal could be opened. Afterward, with the help of Evil-Lyn, Skeletor recovered his sanity and gained control of the Demo-Man, increasing his abilities ten-fold.
Masters of the Universe (2002)
A Keldor action figure was released as a limited edition exclusive at the 2003 San Diego Comic Con. The figure comes with the same weapons as Skeletor, as well as the vial of liquid which dissolved his face. It also features three interchangeable heads: Keldor, Skeletor, and an "in-between" head being burned by the corrosive agent.
Masters of the Universe Classics
The Classics Keldor figure was released in 2010, and included two halves of a purple mold of the Power Sword and the fateful vial.