C'tan

The C'tan originally lived as energy beings that fed on the stars themselves. They are also called star gods or star vampires. They were transferred to the physical world thanks to the technology of the Necrontyr.

The C'tan used the hatred of the Necrontyr towards the Old Ones to help them gather the more subtle living energy they now craved. The C'tan hate psykers and have thus set up a series of 'pylons' on Cadia, which, when completed, will close the Eye of Terror forever, thus blocking most psychic power.

In the war between the C'tan and their now slaves the Necrons against the Old Ones and the younger races, their red harvests started to run dry. Then the Laughing God tricked the C'tan into consuming each other until only 4 remained. Not long after that a plague of Enslavers emerged, which apart from destroying the Old Ones, also depleted the red harvests further. Thus the C'tan decided to enter stasis until life repopulated the galaxy and their harvests could begin again.

The four remaining C'tan are:
 * The Nightbringer (Used to powerful enough to impress its image as that of the grim reaper itself on the psyche of the younger races, apart from the orcs(which is why they do not fear death) but upon entering stasis it was almost destroyed and starved but was released accidentally by Space Marines)
 * The Deceiver (came out of stasis an unknown time ago and has been weaving plots ever since, including the destruction of the Eldar weapons Talismans of Vaul designed to destroy the C'tan on their emergence)
 * The Void Dragon (the most powerful C'tan, resides in stasis on Mars and is rumoured to be the Machine God venerated by the Imperium)
 * The Outsider (A C'tan that went insane due to its consumption of other C'tan, is currently imprisoned in a Dyson sphere under the Galactic plane)

The Inquisition employ elite Temple Assasins, one of which, the ones from the Callidus Temple use a weapon called a C'Tan phase sword. It is unknown what specific relation the weapon has with the C'Tan themselves