King of Castle Grayskull is the second minicomic in the Masters of the Universe series, written by Donald F. Glut with art by Alfredo Alcala. The minicomic was packaged with Man-At-Arms, Mer-Man, and Skeletor's action figures.
He-Man and Battle Cat stop for a moment to consider Castle Grayskull, never realizing that Skeletor is lurking on one of the parapets. Unable to enter the castle, the demon uses his energy blade to conjure an image of the interior. He observes the warrior-goddess Teela, summoned by the Spirit of the Castle to be the guardian of the ancient edifice. Teela is told the legend of a King of Castle Grayskull who will one day unite the halves of the Power Sword to enter the castle and claim its throne. As the Spirit relates this story, it mentions the secret locations of the two halves of the Power Sword.
Upon hearing this discussion, Skeletor vows that he will be the prophesied King of Castle Grayskull, and seeks out the Power Sword. According to the spirit, one half is hidden in Eternia's highest point, so Skeletor journeys to the mountain where Stratos dwells, easily defeating the bird man with his energy blade. The other half is said to be in Eternia's hardest rock, which must refer to the bedrock where He-Man built his home. Skeletor has Mer-Man ambush He-Man, before he can put on one of his "super-power outfits," leaving the way clear for the villains to unearth the half-sword.
With the unified Power Sword in hand, Skeletor's next move is to disguise his fleshless face with grayish clay, to better resemble the colossal visage hewn into the front wall of Castle Grayskull. When he enters the castle, Teela doesn't recognize her enemy, and presumes that he is the King of legend. Once Teela has shown him to the throne, Skeletor reveals his ruse and uses the thrones secret devices to trigger a trap door, sending the woman to the dungeon.
Back at He-Man's home, Mer-Man is still trying to keep the hero preoccupied, but it is a losing battle once He-Man manages to recover his forcefield garment. With the help of Battle Cat, He-Man vanquishes Mer-Man and they ride off to stop Skeletor. When He-Man attempts to force open the Jaw-Bridge, Skeletor decides to control it from within, causing He-Man to be suddenly flung inside. Confronted by "King Skeletor," He-Man refuses to bow, but finds himself outmatched by the awesome power of the throne.
When He-Man awakens, he is with Teela in the dungeon. They agree Skeletor must be stopped before he masters the castle's secrets. Fortunately, the demon failed to remove He-Man's strength garment, allowing him to easily tear his way out of the prison. Skeletor manages to activate the castle's defenses, sending an endless horde of empty suits of armor to attack the heroes. However, in his eagerness to watch his foes fall, Skeletor leaves his coveted throne to get a better view, and while He-Man contends with the lifeless army, Teela catches the demon off-guard and disarms him. Without the Power Sword, Skeletor's control of the empty armor is lost. Realizing his disadvantage, he quickly flees the roof. He-Man tackles him and they both fall to the ground outside the castle, where Battle Cat waits to aid his master. The would-be King of Castle Grayskull runs for his life.
The Spirit of Castle Grayskull speaks to the heroes, telling them that it will now hide the two halves of the Power Sword in another dimension, so that even Skeletor will not be able to find them. The spirit suggests that it may be centuries before the legendary king emerges, and bids the Masters of the Universe to go out and fight evil. However, the Spirit seems to smile, knowing that one day He-Man himself would fulfill the prophecy and take his rightful place as King of Castle Grayskull.
- Although the narration says that Skeletor disguises himself with gray clay in order to trick Teela, the images show him with his yellow skull face.