The Necrons beat the Stormcast Eternals and all of their Gods

This War in Heaven was 65 million years ago and the Necrons and the Yngir won.

The Necrons wiped out all the Old Ones leaving only their handicapped children left. These were the Slann, Aeldari and Orckapes.

The Orckapes were programmed by the Old Ones to be stupid and get stupider as they evolved so they weren't a threat to the Old Ones.

The Old Ones told the Aeldari that if they had too much sex and didn't build a new Web Way they would eventually be defeated.

The Slann were princes that had been turned into frogs by Jesus / Xereus Voo Doo Emporium. The Slann weren't very good at figuring out how the Old Ones technology worked and they went around the Old Ones ruins on Frogger.

Jesus was a child of a Yngir and a human and sought to create a realm in the Immaterium called Heaven where he stored his ultimate angel (God) and other angels so he could control the tree of life at all time zones. But the Yngir lived beyond time and space in the timeless halls and had created the humans that Jesus was born from. The Yngir used the Necron peoples souls and harvested them and then used that energy to win the War in Heaven.