For the first twenty years of MOTU’s existence (1982-2001), Skeletor had no origin. The 1982 mini-comics called him a ‘demon from another dimension’ and left it there. The Filmation cartoon never asked. Then in 2002 the Mike Young Productions reboot quietly delivered the best piece of MOTU lore the franchise has ever produced: Skeletor is Keldor, half-brother to King Randor, transformed when an acid attack destroyed his face and Hordak saved his life by binding a demon to the exposed skull. This retroactively makes the entire MOTU saga a family conflict — Adam (Randor’s son) versus Keldor (Randor’s brother). Every subsequent continuity has preserved this. Revelation visualizes Keldor in flashback. Revolution makes Skeletor’s confrontation with his pre-curse identity a central beat. Mattel has released a Keldor figure in the Origins line. A retroactive worldbuilding decision rarely improves a property as cleanly as the Keldor retcon improved MOTU.
Catalogue source: heman.fandom.com (CC BY-SA 3.0) and contemporary industry coverage.