Planet of Origin: Necrontyr, in the Halo stars regions of the Milky Way
The Necrontyr were a humanoid species which developed an advanced civilisation in the Halo stars regions, on the far reaches of the Milky Way galaxy. Short lived, their bodies blighted and consumed at an early age due the terrible cancers and other illnesses linked to the high levels of ionising radiation given off by their sun. They built in anticipation of their inhabitants' early demise, as the living were only brief residents living in the shadow of the vast sepulchres and tombs of their ancestors. They soon wandered off into space, hopeful to realise their species' potential free from the lethal energies of their birth star. Using stasis crypts and slow-moving antimatter-powered torch-ships clad in the living metal known as necrodermis to resist their millennia-long journeys. They made contact with the Old Ones, a more advanced spacefaring species nearly immortal species, and were astonished to learn that another species enjoyed such long lives while their own were so brutally short.
At the time, the great Necrontyr houses were engaged in civil conflicts known as the Wars of Secession. The Triarch, head of the Necrontyr, realised that the only hope of unity laid in turning toward an external enemy. So they declared war on the Old Ones. The Necrontyr were pushed back to their homeworld where they developed an utter hatred towards all other forms of intelligent life and an implacable determination to avenge themselves upon their seemingly invincible enemies. Then one of their probes investigating a dying star discovered the C'tan entities of pure energy feeding upon the solar flares and magnetic storms of bloated red giants that had little conception of what the rest of the universe was. Diffused across areas larger than whole planets, their minds could not perceive the material universe so the Necrontyr sought their favour and oversaw the forging of physical shells for them to occupy. Incomprehensible forces were compressed into the living metal of the necrodermis bodies which the Necrontyr forged as the full power of the C'tan at last found form. As the C'tan focused their consciousnesses and became ever more aware of their new mode of existence, they came to appreciate the pleasures available to beings of matter and the other realities of corporeal life. The deliciously focused trickles of electromagnetic energy given off by the physical bodies of the Necrontyr all about them awakened a new hunger very unlike the one they had once sated using the nourishing but essentially tasteless energies of the stars. The powers of the C'tan manifested in the physical world were almost god-like and it was not long before the C'tan were being worshiped as the Star Gods the Necrontyr had named them. Perhaps they had been tainted by the material universe they had become a part of, or perhaps this had always been their nature even when they were bound to the suns they fed upon, but they proved to be as cruel and capricious.
With the help of the C'tan, the Necrontyr stood ready to begin their war against the Old Ones anew. The C'tan offered the Necrontyr a path to immortality and the physical stability their race had always craved. Their diseased flesh would be replaced with the living metal of necrodermis that made up their Star Gods' own physical forms. The C'tan swarmed about the biotransference sites, drinking in the torrent of cast-off life energy and growing ever stronger as they glutted themselves on the spiritual detritus of an entire species. It was only when the Silent King, head of the Triarch. emerged from the bio-transference process and looked upon what had become of his people that he saw the awful truth of the pact he had made. In that moment, he knew that the price of physical immortality had been the loss of his soul. The Necrons now enjoyed a unity that the Necrontyr had never known, though it was achieved through tyranny and the complete loss of individuality and emotion rather than by consent. The biotransference process had embedded command protocols in every Necron mind, granting the Silent King the unswerving loyalty of his subjects. He grew weary of this burden but dared not sever the command protocols, lest his subjects turn on him seeking vengeance for the terrible curse he had visited upon them.
The Necron legions set out into the galaxy in their Tomb Ships. Planets were razed, suns extinguished and star systems devoured by black holes called into being by the reality-warping powers of the C'tan. The Old ones colonies were besieged and the species they had nurtured became cattle for the obscene their hunger. As their individual appetites for mortal life energies knew no bounds, the C'tan ultimately began to fight amongst themselves. C'tan eventually devoured C'tan, until only a few were left in the universe. The Old Ones used their great scientific skills to genetically engineer servants with the capability of channeling psychic power to defend themselves and nurtured many potential warrior races, among which Eldars, Rashan and K'nib.
The Old Ones' psychically-empowered servant races spread across the galaxy. The C'tan empire was shattered. For all the destruction they could unleash, they were unable to stop the Old Ones advance but the growing pains and collective psychic flaws of the younger races threw their untapped psychically reactive energies into disorder. War, pain and destruction were mirrored in the bottomless depth of the Sea of Souls. The maelstroms of souls unleashed into the Immaterium by the carnage coalesced in the previously formless energies of the Warp. The Warp gate network of the Old Ones was breached from the Immaterium.Ultimately, beset by the implacable onset of the C'tan and the calamitous Warp-spawned perils they had themselves mistakenly unleashed, the Old Ones were defeated, scattered and finally destroyed. The survivors fled in deep space.
The Silent King then led the Necrons in revolt against the masters. As the C'tan were impossible to destroy, each C'tan was sundered into thousands of smaller and less powerful fragments, then each Shard was bound within a multidimensional Tesseract Labyrinth, Though millions of Necrons had been destroyed, they were once more in command of their own destiny.
The Eldar had survived where the Old Ones had not and the Necrons, weakened by their expenditure of lives and resources in overthrowing the rule of the C'tan, could not stand against them. It would take millions of Terran years for the Eldar's power to fade, but what mattered is that the Necrons would be there to take advantage of it. The Silent King ordered the remaining Necron cities to be transformed into great tomb complexes threaded with stasis-crypts. His final command to his people was to sleep for 60 million years to awake ready to restore the Necron dynasties to their former glory. Then he destroyed the command protocols by which he had controlled his people for so long and took ship into the starless void of intergalactic space, to find whatever measure of solace or penance he could.