The Skeleton King is the main antagonist of the series and the Hyperforce's sworn enemy. His servants include the Formless.
The Skeleton King was originally the kind and humble Alchemist who lived in the region later known as the Zone of Wasted Years. He was a close friend of Captain Shuggazoom, who requested him to make a substitute heroic force, which will later be known as the Hyperforce. At one stage, the Alchemist was studying the Netherworld, which contained a group of evil beings termed by the Verron Mystics as the "Dark Ones". Captain Shuggazoom was at first worried that these evil creatures would breach the barrier the Alchemist created, but he assured him that they were all safe. Unfortunately, Mandarin accidentally caused a breach to occur by jumping on the main console, releasing two of the creatures into the world: a demon-like being who subdued the Alchemist, and a worm like being that would eventually become the Dark One Worm.
Current Skeleton King
After the Alchemist's soul was tainted with evil, he became the Skeleton King. His body turned half skeletal and half machine. The Skeleton King has sworn to destroy Shuggazoom City along with the Hyperforce. He mostly uses Formless to attack, but often creates new creatures to lay waste on the city. As the series advances, Skeleton King broadens his means of attack, going as far as to pursue the Hyperforce at a psychological level. Such as in the episode In the Grip of Evil, where he attacks all of them in a dream.
- Skeleton King's voice actor, Mark Hamill, is known for playing Luke Skywalker in Star Wars and voicing The Joker in the DC Animated Universe franchise. Ironically, He shares much in common with Star Wars antagonists Darth Vader and Emperor Palpatine.
- Though it does not show, Skeleton King still cares for the Monkey Team (his former self the Alchemist, has feelings for them never left after his soul was taken).
- His voice tone was used in Batman the Brave and the Bold as the Spectre in "Chill of the Night"
- He has a room full of Chiro's toys from long ago, indicating an obsession towards Chiro. It could be either he wants to see the boy destroyed, or he could be related to him somehow, perhaps being Chiro's father.
- His armor design was also used on Megatron from Transformers Animated, and his skull like feature is similar to Mon*Star's only more skeletal.
- The Skeleton King's design and color scheme are homage to the 1970s Japanese toy series Henshin Cyborg's villain known as Dokuro King as well as other undead villains Horned King and Skeletor.