Though millennia sped me by from one moment to the next, I saw these star-born Asur grow into a mighty and sophisticated culture. I heard their name sung in a thousand psalms of joy and beauty: The Elder - greater even than the Children of Ulthuan at the height of their power.
[...]
Time moved onwards and I saw the rise of the brother heroes, Eldanesh and Ulthanesh, who alone, in the absence of the First Ones, could control the Warp Gods and summon them onto the physical plane. I saw them march to war against the silver-skinned Yngir, the star gods and their slaves, and I saw them summon dread lord Khaine, The Elder's mighty god of war, to battle with them. I saw the brothers and their god lead their children into battle time and time again, pitting Chaos spawned furies against the soulless technologies of the Yngir.
[...]
In the space of but one generation, the majority of The Elder paused in their quest for enlightenment and chose a darker path of inward-looking excess and debauchery. Daemons and other Chaos entities broke free from the Warp once more, and spread like fire through dry grass across the entirety of The Elder's vast empire.
Some of The Elder renounced the ways of their brothers and sisters, and retreated to their vast city-ships. The Warp-gates that led to the corrupted worlds were sealed shut, and these few noble beings drifted away between the stars. But The Elder that remained behind sank ever deeper into their dark practices. A racial madness had taken them over, an insanity that had only one end.
The Birth of Slaanesh