In the table-top wargame Warhammer 40,000, the Necrons are a mysterious race of skeletal warriors that have lain dormant in their stasis-tombs for millions of years. They are ancient beyond reckoning, pre-dating even the Eldar. Yet, they are beginning to awaken, for the galaxy is ripe for harvest.
Not a lot is known about the origins or the natural history of the ancient race known as the Necrontyr. They seem to be one of the earliest sentient races in the galaxy. What little that is known portrays a bitter race, confined to their homeworld and cursed by drastically short lifespans due to a perilously close orbit around their sun.
The Necrontyr were desperate to free themselves from their tortured lives, and dedicated their scientific advance to two endeavours: studying their sun in search of a defence against its wrath, and planning an escape to another, more hospitable world.
The Necrons' story is one of an ancient betrayal. Aeons ago, the Necrontyr race clung to their short lives in fear of oblivion at the hands of their massive and ravaging star. They pushed the limits of science in an effort to lengthen their lives, but to no avail. Then, the star gods known as the C'tan were discovered, offering immortality at a terrible price.
The Necrontyr agreed, and their souls were encased in living metal bodies. What they did not know was that the process dulled their minds and senses so they became slaves of the C'tan. The C'tan needed warrior-slaves to harvest the life forms of the galaxy so the star gods could feast on souls, and the C'tan's new Necrons served this purpose well.
After countless years of slaughter and the emerging of Enslaver Plague (see below) life across the galaxy ran thin millions of years ago, the Necrons went into stasis, waiting for life to grow back. Now, in the 41st millennium, they have found a galaxy teeming with life again.
In combat, the Necrons are unyielding war machines that bring swift death to their prey. Armed with gauss weapons that strip an opponent's molecules one layer at a time, the Necrons have fierce firepower. Also, they have a remarkable ability to repair themselves, a special rule known as We'll Be Back! This gives the Necrons incredible staying power in a battle, which makes them an enemy dreaded by all races in the world of Warhammer 40,000.
The living metal developed by the ancient and long dead Necrontyr, originally invented for use in constructing their ships. It is a metallic substance that appears to grow and heal as if it were part of a living organism.
It was during their first difficult steps out into the wider galaxy that the Necrontyr 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, where the Necrontyr were impatient, the Old Ones were infinitely understanding and patient beyond belief.
The Necrontyr grew bitter and jealous towards the Old Ones, and it was not long before this jealousy lead the Necrontyr into a futile war against the Old Ones' civilisation. The Old Ones were worlds beyond the Necrontyr in terms of technology, and the attacks by the lesser race were easily shrugged off. But a new discovery about the Necrontyr home star would change this drastically: the discovery of the first C'tan.
The scientists studying the Necrontyr home star had discovered a being of incredible power feeding off its massive energy output. The full weight of Necrontyr science was put behind detailing this discovery, and realising the potential implications such an incredible power might have on the war against the Old Ones. It was not long before other similar beings were discovered, and they were collectively called the C'tan, literally "Star Gods" in the language of the Necrontyr.
The scientists at last managed to communicate with the beings using signals many years long - long enough to be noticed by such a high level of sentience. Using new technologies of living metal, the Necrontyr crafted material bodies for the star vampires, and they invited the C'tan to possess and animate their new material forms.
As the awesome power of the C'tan became material, the Necrontyr began to see these new beings not as guests, but as gods. This suited the C'tan well, as in their material forms they had discovered a new delicacy to absorb that of the living soul, and the flow of power from the Necrontyr towards their new gods was a welcome thrill.
Of course, the C'tan had a hidden agenda. As the Necrontyr entered their immortal bodies, their living essence would escape them, to be easily lapped up by their hungry gods.
In one swift action, the entire Necrontyr race was effectively destroyed, replaced with legions of skeletal robots, who lost the last dregs of their individuality shortly after their transformation. Only a bitter hatred of the living remained. These new beings, from then on known as Necrons, were the ideal minions for the C'tan, and served only to herd the star-gods' cattle, so that they could feed on all life in the galaxy.
During the terrible wars between the C'tan and the Old Ones that followed the grave birth of the Necrons, the Enslavers poured forth into the galaxy, and caused the deaths of many billions of lives. The C'tan, beings of pure physical energy, had no understanding of the Warp, and the onslaught of psychic beings was something they had no ability to oppose. Of course, the Enslavers posed no direct threat to the Necrons or the C'tan, but they were killing the C'tan's cattle in droves, and the star gods and their legions were forced into hiding to wait out this plague.
Nowhere in the galaxy is beyond the reach of the Necrons, as demonstrated by the Mars incident, where five Necron starships passed through the considerable Imperial fleet guarding the Solar System undetected. They were already in the low orbit of Mars by the time the planetary defenses of the Adeptus Mechanicus homeworld could finally register the attack. Although four of the Necron ships were destroyed, the final one managed to land and deliver its unknown content. The fact that five ships managed to penetrate one of the most heavily guarded planets in the heart of the Imperium has dire implications about the previously undoubted impregnability of Holy Terra itself, so this incident is one of the tightly guarded secrets of the Imperium.
What actually happens is that Necron forces strike out of various uncharted tomb-worlds, using their phase technology to rapidly deploy their forces anywhere in the galaxy. When defeated, they simply "phase-out" and return to the tomb-world for repairs. Every Necron fallen in battle can be repaired and re-animated in a tomb-world, so they never actually sustain casualties (although it is possible to destroy these complexes). With more and more Necron awakening from their millennia-long slumber, they are apt to pose a great threat to the whole galaxy.
Other than their military assaults, the Necrons have infiltrated the Imperium to an unknown extent. Their elite anti-psyker troops, the Pariah, are a cross-breed with human genes and it is yet unknown if the Necrons developed the Pariah project by themselves or with the help of Imperial traitors (or possibly even Adeptus Mechanicus). But it is known that the C'tan had the Pariah Gene placed in the human genepool several million years ago. This has since manifested itself in the agents of the Culexus temple, specialist anti-psyker assassins.
Necrons are effectively the souls/consciousnesses of sentient beings (the Necrontyr) trapped in advanced "liquid-state" metallic robotic bodies. Due to being of an extremely high technological level (possibly millions of years ahead of humanity), they are relatively unaffected by conventional EMP weaponry. Whether this is due to radiation shielding or non-electronic components is not currently known. They apparently use portable power cores and teleporters (apparently made up of a greenish crystalline substance) for each Necron soldier.
Another interesting phenomenon is that when a battle has turned strongly against the Necrons, the entire army will simply vanish from the battlefield. Even 'dead' Necrons (those who have not repaired enough to rejoin the fight) and Necrons engaged in close combat will disappear along with the rest of the army, leaving behind their astonished foes. Because of this, enemy forces like the Imperium have had great difficulty in obtaining Necron artifacts or "corpses" to study.
It should be noted that the terms for the weapons and Necrons that follow are given to them by their opponents, not the Necrons themselves. Aside from the C'tan, the Necrons never communicate to non-Necrons; the C'tan known as the Deceiver has been observed infrequently communicating with non-Necrons.
Necron technology is beyond anything the galaxy has ever seen, surpassing even that of the highly advanced Eldar. Their ships are stunningly fast and agile, equipped with propulsion systems which are capable of traveling interstellar distances without entering the Warp. This is achieved, as far as is known, by somehow making their ships unbound by inertia, allowing them to accelerate almost instantly and infinitely, which explains why Necron ships are often seen to be visibly decelerating upon reaching the site of battle. This also protects them from many of the practical problems and dangers of warp travel. All Necron ships are well-armored, equipped with self-repair systems and utilize some sort of advanced stealth technology which makes them difficult to detect for enemy targeting systems, granting Necron vessels surprising staying power overall. Although still devastating, Necron naval weaponry does not seem to match the raw power of some Imperial designs, they are however known to by-pass many conventional defense systems and strike with an unearthly accuracy.
In every battle so far the Necrons could only be defeated by superior numbers, and engaging Necrons on even terms proved to be suicide. Fortunately, all of the Necron fleets encountered so far were small task forces and usually disengaged and phased out like their land-based counterparts, rather than putting up a full fight. But their frequency seems to be increasing, and the possibility of a massive Necron attack is dreaded by the Imperium as well as other sentient races. Even as a raiding force, they are a serious threat, as they are fully capable of outmanoeuvring most other fleets (probably with the exception of Eldar and their dark kin) to pick fights on an even footing. This often leads to catastrophic losses for enemy fleets and forces them to somehow stall with an utterly inferior fighting force for overwhelming reinforcements to arrive, at which point the Necrons simply disengage.
For a list of known Necron spacecraft, see: Weapons, Equipment, and Vehicles of the Necrons.