http://en.wikipedia.org/wiki/Necrons

The Necrontyr

In the universe of Warhammer 40,000, little is known about the origins of the ancient race known as the Necrons. They were one of the earliest races seeded with the Old Ones, appearing only a few million years after the birth of the stars. Their world was scourged by the radiation of the massive, violent star it closely orbited, cursing them to experience drastically short lifespans. The Necrons spent eons expanding their technology in an attempt to extend their lives. Their technology developed Necrodermis, a "living metal", for constructing their ships with which they were able to leave their planet. These slow "tomb ships" full of cryonically frozen Necrontyr were sent to populate the stars over 60 million years ago. It was during their first difficult steps out into the wider galaxy that the Necrons first encountered the Old Ones. The differences between the two races were vast; where the Necrontyr had short painful lives, the Old Ones were blessed with incredible longevity, and where the Necrontyr were harsh, competitive, imperialistic and impatient, the Old Ones were infinitely understanding and patient beyond measure.

The Old Ones tried to help the Necrons in their attempts to expand into the galaxy, but these benevolent efforts were seen as patronizing manipulation and rejected. The Necrontyr eventually grew bitter and jealous towards the Old Ones, and it was not long before this jealousy led the Necrontyr into a futile war against the Old Ones' civilization. The Old Ones had an unmatched strategic advantage in the form of the webway portals which allowed them to outmaneuver the Necrontyr at every opportunity. This significant advantage won out over the Necrontyr's lack of mobility. Then, scientists studying the Necrontyr home star discovered a being of incredible power feeding off its massive energy output. The Necrontyr then bent their studies towards bringing this being into a form which they could interact with.