Second in command of the HailFire Empire and Johnathan Tangelo 's most trusted adviser, the Skeleton King set aside his hatred for the Super Robot Monkey Team in order to save the universes from the many forces who seek to either control or destroy them.
He was once the leader of a group known as the Shadow Force, but lost authority as time went by. Now the Shadow Force is led by multiple villains, though the main leader is Etna, who recently joined the Cosmic Empire.
When Megatron was recruiting Disney villains to join him in conquering the Multi-Universe, the Skeleton King refused the offer. Megatron labeled him an enemy and locked him away. When Johnathan (as the Phantom ) found him in the dungeon, he talked to Megatron about his release. Though Megatron was far from pleased with the idea of freeing an enemy, he finally agreed to John's terms.
It was then that the Skeleton King joined the HailFire Empire and helped John plot against Megatron's tyrannical rule.