Skeletor was formerly a warlord known as Keldor who trained under Hordak. He gathered a small band of warriors to attack the Hall of Wisdom. They encountered resistance from Captain Randor and his officers; Keldor fought Randor personally, wielding two swords with astounding proficiency, but when Randor disarmed him, Keldor threw a vial of acid at him. Randor deflected it with his shield, and the acid splashed on Keldor's face.
Kronis called the retreat, and Evil-Lyn took Keldor to Hordak's sanctuary, where Keldor summoned Hordak to save his life. Keldor agreed to pay whatever price Hordak wished for his life, and Hordak transformed him, stripping the damaged tissues from his skull and dubbing him Skeletor; Keldor's head had been completely stripped of soft tissues, leaving only a floating skull. When Keldor saw his new appearance, he laughed maniacally; the incident perhaps shattering whatever sanity he had left.
Trapped in the Dark Hemisphere by the Mystic Wall, Skeletor designed a machine that would smash it, but it needed the Corodite Crystal as a power source. When Mer-Man retrieved it, Skeletor destroyed the Mystic Wall, and returned to menacing Eternia.
Unlike this previous portrayals, Skeletor is not concerned with Castle Grayskull right away, until a giant fish-monster heads toward it and the Eternian warriors led by Man-At-Arms and He-Man stop it, forcing Skeletor to ponder what could be in that ancient pile of stones worth dying for. At the time, the Heroic Warriors seem ready and willing to let Grayskull fall, and would likely have done so, if not for the urgings of Man-At-Arms, who had been swallowed whole by the monster. Skeletor directly attacks it with his Council of Evil: himself, Count Marzo, Evilseed, the three evil Giants and Webstor. When King Hiss and the Snake Men are freed from the Void, Hiss imprisons Skeletor, having him devoured by a giant snake, but Skeletor escapes after the Masters defeat Hiss.
Despite owing his life to Hordak, Skeletor destroys Hordak's sanctuary to prevent him from returning. At the end of the Second Season, King Hiss revives Serpos, the Serpent God, who had been transformed into Snake Mountain by the Elders; Skeletor and his minions were inside the mountain at that time. Although Serpos is defeated and restored to its Snake Mountain form. If season three of the series been produced, it would have seen Skeletor and He Man dealing with the Horde invasion and the powerful Hordak, who it was said Skeletor eventually defeated.