Mumm-Ra is an undead sorcerer that serves as the main antagonist of the ThunderCats franchise.
The evil Mumm-Ra has lived upon Third Earth for over a thousand years, maintained by the dark power of the Ancient Spirits of Evil. As the emissary of the Ancient Spirits, Mumm-Ra carries out their will by commiting heinous acts against the peoples of Third Earth. Ever since the Thundercats arrived on Third Earth, Mumm-Ra has made their destruction his primary goal as their code opposes everything that the Ancient Spirits stand for. In order to achieve this goal, he has used his vast magical abilities to attack the Thundercats both directly and covertly, often concocting devious schemes to confuse and disarm them. He has also conspired with other enemies of the Thundercats, such as the Mutants from the planet Plun-Darr and the Lunataks.
Mumm-Ra fears the power of the Eye of Thundera, the magical stone embedded within Lion-O's Sword of Omens. He is determined to take the sword for himself, either to use it against the Thundercats or simply to destroy it. His plans have always been foiled, but being immortal, time means nothing to Mumm-Ra and so he can simply wait for the right opportunity to arise.
In the modern ThunderCats cartoon, Mumm-Ra's origins are explored in greater detail. Once a mighty interstellar warlord, he roamed the universe in search of four Stones of Power, bringing planets to their knees and enslaving various animal races in his quest to find them. He intended to bring order to the universe by uniting all beings under his dominion. When Mumm-Ra's forces eventually found each of the stones, Mumm-Ra's lieutenant Leo - the ancestor of Lion-O - betrayed him and incited a rebellion aboard Mumm-Ra's pyramid ship. The evil sorcerer was robbed of the stones and stripped of most of his power, and so he retreated to the sanctity of his sarcophagus. However, Leo and the rebelling animals damaged the ship's controls, leading to the vessel crash-landing on Third Earth and Mumm-Ra being unable to escape from his sarcophagus.
Following the animals arrival on Third Earth, the races divided and sought to make their own way of living on this new planet. No single race could be entrusted with the Power Stones, and so each of the four stones was taken into custody by a different race. The Spirit Stone went to the Elephants, the Birds used the Tech Stone to establish an advanced skyborne society, and the War Stone was taken by the Cats who would come to build the strongest empire on Third Earth. Meanwhile, Mumm-Ra was trapped within his pyramid, unable to get out of his sarcophagus. He would remain there for centuries until the day that Panthro and Grune, two generals from the kingdom of Thundera, ventured into the Sand Sea on their search for the legendary Book of Omens. Mumm-Ra telepathically reached out to Grune, finding it easy to corrupt him due to the general's desire for power. He promised Grune power beyond his wildest dreams and lured him toward his pyramid, showing the Cat general how to enter the structure and demanded that Grune release him from his confinement. Ignoring Panthro's words of caution, Grune forced the sarcophagus open and Mumm-Ra was released.Upon his release, Mumm-Ra disposed of Panthro and he and Grune immediately went to work plotting the conquest of Third Earth. With trickery and cunning, Mumm-Ra was able to gather resources to build a new army and approached the Lizard nation in order to recruit them. The Lizards had been struggling to survive since they were constantly being repressed by the Cats, and so they were all too eager to take revenge and remove the Cats from the top of the food chain. Mumm-Ra provided the Lizards with technology that would allow them to easily dominate the Cats and most other races, since technology was extremely rare on Third Earth. With his new Lizard army, Mumm-Ra was able to launch an invasion of Thundera which saw the kingdom reduced to ruins and King Claudus slain. Knowing that the Cats possessed the War Stone - which they now referred to as the Eye of Thundera - Mumm-Ra attempted to take the Sword of Omens. However, the Thunderian clerics had long ago placed an enchantment upon the sword that protected it from evil hands, and so Mumm-Ra could not touch it. He tried to force the high cleric Jaga to remove the spell, but the sword was taken by Lion-O with the aid of his adoptive brother Tygra and the cleric Cheetara. These new ThunderCats escaped Thundera in order to find the Book of Omens, which would hold the key to defeating Mumm-Ra.
Mumm-Ra's armies would pursue the Thundercats all across Third Earth in order to retrieve the Eye of Thundera. The Thundercats would eventually find the Book of Omens as well and they would use it as their compass for finding the other Power Stones. The Cats would manage to acquire the Spirit Stone, but Mumm-Ra would later acquire the Tech Stone from the treacherous Bird prefect Vultair. The whereabouts of the fourth stone are unknown.
"Ancient Spirits of Evil, transform this decayed form...to Mumm-Ra, the Ever-Living'!'"In his standard form, Mumm-Ra appears as a withered husk, with dead gray skin, jagged rotten teeth and glowing blood-red eyes. His body is wrapped in bandages and he wears a tattered red robe that drags along the ground as he walks.
When Mumm-Ra transforms into his "true form", his body grows larger as his muscles expand. He has less bandages and wears a warrior's helmet upon his head as well as greaves on his forearms and pauldrons on his legs. In the 1985 ThunderCats series, Mumm-Ra's robe forms into a cape that resembles bat-like wings and a tattoo of a twin-headed snake appears on his chest. In the 2011 series, the emblem is not a tattoo but rather a piece of armour attached to Mumm-Ra's chest, and instead of a cape he has actual wings protruding from his back.
- Black magic - Mumm-Ra is a master of the dark arts and frequently uses various spells and artifacts with which to confound the ThunderCats. In battle, he often casts blasts of magical energy from his hands.
- Flight - Mumm-Ra has been capable of flying in both series, but only in the 2011 series has he used proper wings.
- Immortality - As his title implies, Mumm-Ra lives forever and cannot die, at least not premanently. He has appeared to have been destroyed on more than one occasion, but he always ressurrects back inside his sarcophagus. With each ressurrection, Mumm-Ra seems to gain more power.
- Shapeshifting - In both series, Mumm-Ra has demonstrated the ability to magically alter his appearance. He frequently takes on the forms of innocent beings or allies of the Thundercats in order to lull them into a false sense of security. He even turns into animals and has often taken the form of a crow in the 2011 series.
- Sword of Plun-Darr - Mumm-Ra's signature weapon is a double-edged sword that he can wield to great effect. The origins of the sword have varied between continuities. In the original series, the sword came from the planet Plun-Darr and was wielded by the ancient Mutant warlord Rattila, but wound up on Thundera following a war that the Mutants lost. In the 2011 series, Mumm-Ra created the sword himself from metal taken from the core of a dying star. When Mumm-Ra's ship crashed on Third Earth, the sword was buried deep in the mountains of Plun-Darr until discovered by the Thundercats, only for Mumm-Ra to steal it shortly after Lion-O found it.
- Armor - In two episodes of the 2011 series, Mumm-Ra has donned a suit of armour that is both magical and technological in nature. The armour is created when the four Power Stones are used in tandem with the Sword of Plun-Darr and its gauntlet. This armour magnifies Mumm-Ra's powers significantly and also increases his size.
- Telepathy - Mumm-Ra has also been known to invade the minds of others, forcing information out of them or corrupting them to serve him.