The Necrons

"Throughout the final stages of the War in Heaven, Szarekh bided his time, waiting for the moment in which the C’tan would be vulnerable. Though the entire Necron race was his to command, he could not hope to oppose the C’tan at the height of their power. Even if he did, and somehow met with success, the Necrons would still then have to finish the War in Heaven alone. No, the Old Ones had to be defeated before the C’tan could be brought to account for the horror they had wrought. And so it was that, when the C’tan finally won their great war, their triumph was short-lived. With one hated enemy finally defeated, and the other spent from hard-fought victory, the Silent King at last led the Necrons in revolt against the star gods.

In their arrogance, the C’tan did not realize their danger until it was too late. The Necrons focused the unimaginable energies of the living universe into weapons too powerful for even the C’tan to endure. Alas, the C’tan were immortal star-spawn, part of the fundamental fabric of actuality and impossible to destroy entirely. So was each C’tan instead sundered into thousands of fragments. Yet this was sufficient to the Silent King’s goals. Indeed, he had known the C’tan’s utter annihilation to be unachievable and had drawn his plans accordingly: each C’tan Shard was bound securely within the extra- dimensional space of a tesseract labyrinth, unable to escape. Though the cost of victory was high – millions had been killed as a consequence of rebellion, including all of the Triarch save the Silent King himself – the Necrons were once more in command of their own destiny."

Codex Necrons 8ed p9