Hordak

Arrived on Eternia while battling He-Ro
Raised an army, then challenged the Snake Men for rule over the planet
Defeated King Hiss, banished to the dimension of Despondos by King Grayskull
Freed centuries later by Keldor, later trained him in the use of dark magics;
Erased his memories when the Havoc Staff turned him into Skeletor
Returned to Eternia, tried to conquer the planet but was again defeated
Kidnapped baby Adora & escaped to Etheria, raised her as a member of the Horde
Attacked & conquered that world, opposed by the Great Rebellion
Originally a great sorcerer, but chose to rely on tech, integrated it into his physiology