The Ancient Spirits of Evil are dark evil spirits, each normally residing within four possessed statues that represent various evil animals (Monkey, Jackal, Lizard, and Vulture) within the Black Pyramid. Their statues surround the Well of Souls within Mumm-Ra's chamber.
Not much is known about the Ancient Spirits other than that they give Mumm-Ra the means to assume Ever-Living form and various other powers. The Ancient Spirits also played a part in directing Mumm-Ra into gathering the materials to create the Sword of Plun-Darr while they possessed a Blacksmith so they can use his body and skills to forge the actual weapon. However, as the Blacksmith retained the knowledge of forging the Sword of Plun-Darr from the possession, the Ancient Spirits played an unintended role in the creation of the Sword of Omens
In the aftermath of Mumm-Ra's defeat and the Power Stones divided among the Animals, the Ancient Spirits are reduced to being worshipped by the Tiger Clan, the only branch of the Thunderian race who remained loyal to Mumm-Ra and were exiled for their prideful arrogance. Eventually, two decades before Mumm-Ra's release, the Tiger Clan is inflicted by a plague and their leader Javan beseeched the Spirits' aid. The Ancient Spirits respond to the Tigers' plight and remove the disease, asking for payment in the sacrifice of Javan's newborn son, who they saw to someday become a threat to them - Tygra.
However, Javan could not bring himself to kill his son and instead sent him away to Thundera for safety. This is turn forces the enraged Ancient Spirits to reintroduce the plague to kill off the entire Tiger Clan and then curse their spirits to remain in the cave as shades that turn into mindless Shadow demons at nightfall. The curse lasted for years until Tygra's return, in which both becoming humbled and the love for his father broke the curse and enabled the Tiger Clan to pass on.
- The Original series had different animals representing them, three of which were a Boar, a Crocodile, and a Bull. The new series replaces them with a Lizard, an Anubis-based Jackal, and an Ape. Both versions have the fourth being a Vulture, with the reboot version having elements of various bird-headed Egyptian deities in its design. The new series versions of the spirits are a reference to Mumm-Ra's generals: Slithe, Kaynar, Addicus, and Vultaire.