Evil undead sorcerer of Third Earth who worships Spirits of Evil. Arch-enemy of Lion-O and the Thundercats. Although he is usually a shriveled corpse within his stone sarcophagus, he invokes the Spirits of Evil to infuse himself with immense power, becoming Mumm-Ra the Ever-Living. In this form, he is nearly undefeatable, but for one minor weakness - he cannot abide the sight of his own face.

Mumm-Ra is dedicated to eradicating the Thundercats, and will do everything in his power to achieve that goal. He often works with Slythe and his band of evil mutants.