Sumerian An, Akkadian Anu, the sky god and nominal head of the Mesopotamian pantheon, remote from the action of most myths and rarely the agent of anything in them. His rank number in the sexagesimal god-list is 60, the highest.
In the texts
He presides rather than acts. In Atra-Hasis Epic the gods cast lots and Anu goes up to heaven while Enlil takes the earth; in the Enuma Elish he is of the older generation that the younger gods supersede. The Anunnaki, on the standard reading of the name, are his offspring, which is where the term comes from.
In the ancient-astronaut reading
Zecharia Sitchin makes him the ruler of Nibiru and the rank numbers a chain of command, with Enlil at 50 and Enki at 40. That reading depends on the numbers being an organisational chart rather than a sexagesimal notation, and on a translation of Anunnaki as those who came down from heaven that the standard lexica do not support; Michael S. Heiser set out the objection in detail. The node exists because the vault carried the Anunnaki, Nibiru and four Sitchin book entries without a single figure from the pantheon they concern.
Connections
Anunnaki · Enlil · Enki · Enuma Elish · Atra-Hasis Epic · Zecharia Sitchin · Nibiru · Michael S. Heiser · Ancient Astronaut Hypothesis