Old Ones

The Old Ones were an extremely advanced and powerful tech-sorcerer race of beings back when the grass was green and the Emperor wasn't born yet.

Then they met the Necrontyr, and all hell broke loose.

The Necrontyr, being miserable piles of shit with miserable short lives envied the Old Ones and started to war against them.

The Old Ones fucked them seven ways 'till Sunday until the Necrontyr, who realised they were not strong enough to win, discovered the Star-Gods, the C'tan. Blah blah sacrifice our souls and live as cold metal automatons blah blah fight the Old ones.

At this point the Old Ones supposedly created other races to row row fight the Necrons: The Eldar, the Orks and the Jokaero.

In the outcome, the Necrons and their C'Tan overlords were forced(?) into hibernation and the new and young races survived.

The Old Ones themselves, seeming to have done one Acid strip too many, promptly disappeared from the scene.