Slaves to Darkness are the mortal followers of the Chaos gods, from barbaric warriors riding across burning plains or hidden cultists plotting the downfall of their own city. Their tribes are the most prevalent human culture in the Mortal Realms, with many of them numbering in the hundreds of thousands.
Across all the Mortal Realms creatures of all races and hues may turn to the dark gods. Many are their reasons and excuses but their path can only end three ways: by death, by becoming a Chaos Spawn or by ascension to immortality as a Daemon Prince.
The vast majority of them are not necessarily evil and are still humans that feels all emotions and experiences. But their gods and the acts performed in their service are fundamentally corrupting. To rise among the ranks of the Slaves to Darkness is to truck with daemons and sorcerers, courting fell powers from beyond and basking in their fickle attention. The power of Chaos is not to be used for noble causes and those who do will find their soul remade as the gods’ plaything due to the nature of Chaos being to despoil and defile even the purest of intentions. Worshippers of Chaos are eternally bound to walk a road that leads to their own demise, or being remade in the image of their god for evermore and losing the essence of who they once were. Thus the price of walking the Path to Glory is always the soul. As a result all those who bear the brand of Chaos are "Slaves of Darkness', All, but their leader, the Three-Eyed King, Archaon the Everchosen.