The Dark Gods are the four monstrous entities that rule the Warp, better known collectively as the Chaos Gods. Each was born and is sustained by a particular facet of mortal emotion, growing ever stronger as the sentient races of the galaxy rage, despair, scheme, and hunger.
Khorne, the Blood God, embodies wrath and slaughter; Nurgle, the Plague God, feeds on despair and the stubborn will to endure; Tzeentch, the Changer of Ways, thrives on ambition, hope, and intrigue; and Slaanesh, youngest of the four, is born of excess and unchecked desire. Together they are sometimes named the Ruinous Powers, and their combined influence is the single greatest threat to every living thing.
Though the Dark Gods are worshipped by countless cults and championed by the Chaos Space Marines, they care nothing for their servants beyond the emotions and souls they harvest. To bargain with them is to be used and, eventually, discarded. They are not gods of a faith that offers salvation but predators of the soul, and the Great Game they play is one in which mortals are only ever the pieces.