Chaos And The Warp Lore

Demons are deformed creations of the warp in service to the 4 chaos gods Korne, Tzeentch, Slaanesh and Nurgle. Nurgle is the chaos god of filth, pestilence and disease, Korne is the chaos god of blood and Carnage, Tzeentch is the god of deception and deceit and Slaanesh is the god of temptation and ecstasy. All the chaos gods have their own types of demons and devote chaos space marines such as korne bezerkers (korne), noise marines (slaanesh), plague marines (nurgle) and rubic marines (tzeentch) and demons like bloodletters and bloodthirsters (korne), great unclean one’s and nurgglings (nurgle), lords of change and screamers (tzeentch), demonettes and keeper’s of secrets (slaanesh).
 
Each demon is a shard of its own god and can be absorbed by its god whenever it wishes.
There are 3 types of demon a normal demon spawn with no purpose other than to serve its god, a daemon prince which is a follower of the gods that if it pleases the god than will be rewarded with a demonic ascension and the greater daemons which are more powerful daemons that require an actual body in-order to enter the living world and carry great authority.

The Chaos Space Marines

The Chaos Space Marines were originally formed at the beginning of the horus heresy were one of the emperor’s sons horus was manipulated by the Primearch Lorgar to being infected by a Nugle infected blade and eventually turned against his father with his army of chaos space marines forming the first traitor legion.

Over the past 10,000 years there have been an increased amount of traitor legions, guardsmen and titans. Some of the most devout servants to the dark gods are gifted with ascension to a demon prince of chaos.