The Custodians (カストディアン Kasutodian?), also known as the Anunnaki (アヌンナキ Anun'naki?), are a race of highly advanced space-faring extraterrestrial beings who created and ruled over prehistoric humanity, the Lulu Amelu, and were responsible for the Curse of Balal.
The Anunnaki are a group of deities appearing in Sumerian, Akkadian, Assyrian and Babylonian mythologies. Descriptions of their number and role vary between tales, from gods of the heavens who created and decree the fates of humanity to judges residing in the underworld.
In the ancient past, before humanity existed, the Custodians arrived on Earth using interstellar cruise ships such as the Frontier. They attempted to create life with their first prototype, Adam Weishaupt, but due to being created "perfect" with no potential for growth or evolution he was cast aside and forgotten. Later on, they attempted to create life again using both qualities they liked and disliked, resulting in humanity, which they accepted. They appear to have acted as deities to pre-historic humanity, specifically Sumerian and Babylonian civilizations, and either through gifting it or some other means their highly advanced technology and the means to replicate it came into the hands of humanity.
At some point the ancient priestess Finé fell in love with the Custodians, who she believed to be a single god, and in an attempt to stand on equal ground and communicate with them she and humanity began to construct the Tower of Babel. The Custodians saw this as the Lulu Amelu finding a way to make themselves stronger, which the Custodians saw as a threat and a sign of disrespect. In response, the Custodians destroyed the Tower and converted the moon into a device that emitted the Curse of Balal, which robbed humanity of its Unified Language and prevents mutual understanding. After this incident the Custodians appear to have stopped all contact and interactions with humanity, and possibly have left the planet or solar system.
The only shown Custodians are the unnamed "Holy Corpse" (potentially named Shem-Ha) who was buried in Lake Vostok, and Enki, who was shown activating a "network jammer", and apologizing to Finé before collapsing due to his heavy wounds.