Daemons

Daemons are malignant entities that live in the Warp, and act as extensions of their Chaos God. They are purely immaterial beings and can only enter realspace in the following ways: Daemons are functionally immortal, and return to the warp when 'killed'. This immortality is why Chaos champions seek to become Daemon Princes. However, they can be imprisoned within an object, or permanently killed under the right circumstances. Saying the daemon's true name severely weakens them; this is also true of Daemon princes, including the traitor Primarchs, as their true names were given to them by the Emperor before they were kidnapped by the Chaos Gods.
 * Summoning by a ritual (such as a blood sacrifice)
 * Possession of an unprotected Psyker
 * Crossing through a Warp rift, especially Warp storms

Types of Daemons
Khornate Daemons are known as Bloodletters and Bloodthirsters. They are hyper-violent and will destroy everything in sight. They will even attack their own side if there aren't enough enemies to slaughter, for Khorne does not care from where the blood flows. Nurglite Daemons are known as Nurglings, Plaguebearers, and Great Unclean Ones. They spread disease and contagion, and are highly immune to pain and destruction, but are also very sloth. Nurglite Daemons are very friendly by comparison, though their idea of friendship includes sharing horrifying plagues. Tzeentchian Daemons are known as Pink Horrors and Lords of Change. They are magically adept and can change reality on a whim. They are known to be very manipulative and orchestrating various schemes to bring down the ruin of others. Slaaneshi Daemons are known as Daemonettes and Keepers of Secrets. They seek out extreme emotions and sensations, dealing and receiving both pleasure and pain. They are also very fast and agile, but physically frail. As Leman Russ demonstrates, its possible to kill a daemonette by depriving it of sensation - in his particular case, blue-balling a daemonette. Some unaligned daemons exist, such as Furies. Malal does not officially have Daemons, though because he doesn't exist it doesn't really matter.
 * Members: Skarbrand
 * Members: Epidemius
 * Members: Kairos Fateweaver
 * Members: Masque of Slaanesh
 * Members: Be'lakor, Mayor Brimstone