The Annunake are an ancient race of interstellar conquerors who built an empire, tens of thousands of years ago. When the human-like Hunter/Gatherers were colonizing the stars, the Annunake waged a war of conquest to subjugate their colony wars. One of those worlds was Earth, but due to the Annunake fighting on many fronts and the level of resistance on Earth itself they abandoned the fight for Earth leaving several observation ships on the world.
One of those observation ships was responsible for the flooding / submerging of the city of Atlantis. Eventually the Annunake conquered by Hunter/Gatherers, who became slaves and warriors of the Annunake Empire. By the 20th century, the Annunake and Hunter/Gatherers had become one people within the Annunake Empire.
Being a spacefaring race, the Annunake have interstellar vessels and energy weapons. The Annunake Empire has skull-shape warships the size of cities. The Observation Ships left behind on Earth, were sentient and miles wide.
Annunake have a humanoid form with a humanoid face, hair, scales, claws, and a tail. They are able to shapeshift, including growing leather wings, changing into a draconid form, or transforming into a winged dragon that is over a 100 ft long. Annunake also have the ability to project a stream of flame from their mouths.