Chaos is the name for the primordial forces that exist within the warp. It is lead by the four Chaos Gods Khorne, Tzeentch, Nurgle, and Slaanesh, and is fundamentally opposed to the Emperor and his Imperium.
The Warp Edit
Beyond the material realm exists the Warp, a place where all the thoughts and emotions of soul-bearing species collect and coalesce. Physical laws break down in the Warp, making it useful for space travel, but also makes it extremely dangerous. Those without protection will find themselves driven insane, or worse, became prey to the inhabitants of the Warp, known as Daemons.
The Warp will sometimes also merge with the material realm in what's known as a Warp Storm. Most storms are temporary, but one of the largest and most dangerous of Warp Storms is the Eye of Terror; most of the Traitor legions hide out in here. The Eye of Terror is located where the Eldar empire used to be before the birth of Slaanesh. Chaos' ultimate goal is to permanently merge the material and immaterial realms to do with as they will.
Forces of Chaos Edit
The four Chaos Gods represent different experiences and emotions, and are often at war with one another whenever they lack a common goal. They are served primarily by daemons as extensions of their own will, though they are also served by mortal followers who will serve them in exchange for favor. Those with the highest favor will become Daemon Princes and become effectively immortal.
Most of Chaos' servants come from three different factions: