Hordak is an ancient evil sorcerer of unknown origin who battled both Castle Grayskull's original ruler, King Grayskull and the Snake Men ruler, King Hsss with his Evil Horde army. At some point, Hordak invoked the great Spell of Separation, separating Eternia into Light and Dark Hemishperes.
Ultimately defeating the Snake Men, Hordak turned his attentions toward King Grayskull's kingdom. Hordak commanded his Horde Wizards to draw Castle Grayskull into the dimension of Despondos. The spell failed with King Grayskull's intervention, only destroying the area around the castle and drawing Hordak and his army into Despondos instead. However with one final act, Hordak's powerful spirit delivered a mortal blow to Grayskull before being sucked into imprisonment.
Centuries later, Evil-Lyn invoked Hordak's mystical essence in Despondos to save Keldor's life after his battle with Captain Randor. Hordak saved Keldor from the acid by magically transforming Keldor, but only on the promise of a later price to be paid. Hordak christened the transformed Keldor "Skeletor".
Shortly after the reappearance of King Hsss and the Snake Men, Hordak causes physical pain upon Skeletor and calls upon him to free him from Despondos. Skeletor travels to Hordak's temple, seemingly to free Hordak. Even He-Man assumes that Skeletor's reason for going to the temple was to free Hordak. However, Skeletor surprises both He-Man and the onlooking Evil-Lyn by defiantly destroying Hordak's temple, thus seemingly ridding himself of Hordak forever.
Soon Evil-Lyn attempts to free Hordak through a different place of power, the Well of Darkness. She blackmailed Count Marzo into assisting her by holding his amulet, but after He-Man destroyed the Well of Darkness, Marzo betrays Evil-Lyn, backhanding her and regained the power of his amulet.
Hordak's mastery of the dark arts was so powerful that he rarely needed to move in combat, preferring to rely on his great mystic power. He was even able to execute one of his generals, Callix for questioning him without moving a muscle. Similarly to Serpos, the colossal Snake God of the Snake Men, Hordak also had a spiritual form of great power. Once his physical form was removed from the material plane of Eternia, his spiritual form remained, suggesting that it was this form, not necessarily his physical form that needed to remain on Eternia. The full capabilities of these spirit forms are unknown.
Hordak was intended to be the main villain in the third season of the cartoon series. According to Ian Richter of Mattel, who initiated most of the storylines on the cartoon, Hordak was going to conquer Eternia in season three and serve as the main villain of the season before finally being overcome by Skeletor. However, the toy line and cartoon series were both canceled after the show's second season, so the third season was never produced.