Daemon

A Daemon is a manifestation of a negative emotion in the Warp. They can be summoned as warriors by the Minions of Chaos.

Some Eldar deities appear to be a sort of Daemon, but much, much kinder and benevolent.

Life Cycle
Daemons do not "live", per se', but there is a progression of existence.
 * 1) Manifestation
 * 2) Self-Sustenance: If the emotion is strong enough, it becomes permanently manifest in the warp, and can be summoned into "reality" to fight. However, it cannot remain there for long.
 * 3A) Chaos Spawn: A Daemon who possesses an unfortunate human. They mutate horribly.  The daemon's psychic powers are diminished, but are still formidable.  Psykers are particularly vulnerable, while "Blanks" are completely immune.  Corpses however have no resistance whatsoever, and even the body of an Emperor-fearing space marine can be possessed.  If a human makes a deal with a daemon, the mutations are controlled, usually bringing forth wings and claws.
 * 3B) Greater Daemon: A greater daemon is a huge beast; depending on the emotion, it will be either a Keeper of Secrets, Bloodthirster, Great Unclean One, or a Lord of Change.
 * 4) Godhood: Only seven have reached this state. These are: Tzeentch (magic, arcane wisdom, hope, selfish ambition, and change), Nurgle (gluttony, excess, and disease), Slaneesh (lust, depravity, and deception), Khorne (blood fury), Malal (revenge, infighting, and anarchy), Zuvassin (misunderstanding, screw-ups, sabotage), and Necoho (Atheism). They are the ultimate embodiment of the emotion that spawned them.

Alternate Cycle
An extremely loyal follower of a chaos god can gain enough favor to "ascend" to daemonhood.

One of Nurgle's diseases causes the body to rot out from under a being's soul, and he then claims the freed soul and fashions it into a Plague Bearer. Those infected who choose to be loyal to the Imperium usually undertake Death Quests, placing themselves in mortal danger to be freed from ownership by one of the "dark gods".