The Anunnaki are a refugee group From Sirius. The Most Known are Anu, the Father; Enki and Enlil, the Brothers; and Ninsun, the sister, more descendent we know as Marduk, Inanna, and Gilgamesh, Afcaurse these are not all the names.
During and after the Galactic War, Refugees from all Corners of the War fled to the safe haven of Sirius; after the War, a Group of These Refugees decided to explore the universe independently. They eventually settled on a planet called Nibiru. Millions of years later, having many internal conflicts, with kingdoms and empires rising and falling, the ANU Family Became Supreme power, and The new civilization became known as the Anunnaki.
When the planet's atmosphere failed, and the earth Died, they needed a lot of gold to refine into gold particle dust to repair the atmosphere. They searched and exploited the galaxy for this resource and eventually found the earth, a literal gold mine. So they settled here for some time, Creating us humans from the local species to do the mining for them.