Necrons

The remnants of the ancient race known as the Necrontyr, these beings worship godlike entities known as the C'Tan, who feed on the life energy of the living. Aeons ago, the Necrontyr agreed to have their life-essences housed withn shells of living metal, in effect making them immortal, in order to better serve their masters. The Necrns harvested untold bllions of souls for the C'Tan, in turn contributing to a drastic reduction in the C'Tan food supply. Because of this, the C'Tan retreated to stasis, guarded by their metalic slaves, for some sixty million years.

Now, n the forty-first millennium, with their overlords' "food source" replenished, the Necrons have begun to reappear. Feared by all living races, the Necroms seem to materialize out of nowhere, and disappear just as mysteriously. Becaue of this ability to phase out, when struck down on the battlefield or the tide of the battle seems to be turning against them, the Imperial forces never have been able to secure a Necron specimen -- alive or dead. In addition, Necrons appear and wage war in total silence, communicating only in the presence of others of their own kind.