According to the opening show's narrative, Mumm-Ra, a sorcerer and demon-priest, is an ancient native from Third Earth, serving as the undead focus for the Ancient Spirits of Evil--four god-like entities of nearly unlimited power, but whose influence is limited to the Black Pyramids found on either Third Earth or New Thundera. As such, outside of either pyramid, they can only interact with the physical world through Mumm-Ra. They provide him with immortality, as granted through his sarcophagus in exchange for perpetual servitude.
Mumm-Ra usually resides in his Black Pyramid as a withered, corpse-like being; however, he can alter his form by reciting the following incantation: "Ancient spirits of evil, transform this decayed form to Mumm-Ra, the Ever-Living!" This transforms him into a muscular fiend who menaces the ThunderCats with episode-long challenges before being driven back into his sarcophagus. In later episodes, while endowing Mumm-Ra with his powers, the statues of the Ancient Spirits of Evil come down from their perches, extend their arms over him as the powers of evil flow into Mumm-Ra.
SCULPTED AND PAINTED BY TOYMAN ARTIST RAY DANOS