Setekh is one of the Necrons, a mysterious race of skeletical robots that are ancient beyond reckoning, predating mankind, the Eldar and even the Gods of Chaos. At one point, they used to be known as Necrontyr, mortal beings blighted with sickness and extremely short lifespans. To remedy this, they struck a bargain with the energy beings that fed on stars called C'Tan, who would grant the Necrontyr immortality by placing their essences in metal constructs and, in turn, they would serve the C'Tan as their undying, soulless slaves. The Necrons waged a conflict known as "War in Heaven" against their enemies, the Old Ones and all life in the galaxy, harvesting their souls for their masters to devour. At the end of the conflict, they turned on the C'Tan shattering their physical bodies into small shards and going into hibernation until such a time where they could rebuild their forces and the dynasties of the Necrontyr could rule the galaxy one more. For millions of years the Necrons have slumbered, waiting out their old enemies and now they are waking up into a galaxy teeming with new life forms.
The Necrons dwell on tomb worlds scattered across the galaxy, each containing complexes of countless inert Necron warriors. Once they awaken, or are disturbed by foolish trespassers, they set about harvesting and cleansing their surroundings of all life, down to the bacteria if necessary. Their grasp of technology surpasses even the Eldar, and the Necrons are able to teleport seemingly at will. Their weapons are hideously effective, using Gauss technology that strips a target's molecules apart one layer at a time, while the living metal that forms their bodies can regenerate from just about any injury. Setekh was regarded as one of the mightiest Necrons to exist and he was emtombed the Space Hulk Kronos for 60 million years.
During the Age of Imperium in the 40th Millennim, two Ordo Xenos factions were racing against each other to find Setekh - one lead by Inquisitor Malva, who sought to locate and examine the Necron technology for its own means and opposed to him was Inquisitor Jena Orechiel, who wanted to destroy the Necron tech from keeping to be used against the Imperium. Jena enlisted the help of her estranged son Kal Jerico, while Malva recruited the Deathwatch Space Marines. The confrontation between the two groups upon his tomb disturbed Setekh from his slumber.
Setekh was truly a horrifying opponent as he proceeded to slaughter the Deathwatch squad (as if they were mere whelps with its vaporizing blasts, and as noted by Jena, he was extremely weakened by the time he awoken after millions of years, a mere shadow of his full power and it was only a matter of time he would recover it whilst drawing energy from his sarcophagus. Despite her retinues' best attempts at slowing down the behemoth by destroying its regeneration chamber, he was just too powerful to be contained and decided to teleport back to their ship and ordered Exterminatus upon the Space Hulk, firing cyclonic torpedoes against Setekh who seemingly perished. One must wonder and dread what would Setekh would have been capable of in his full capacity, as not even the Deathwatch (the most prestigious elite among all Adeptus Astartes) were a match for them, and nothing short of orbital bombardment reserved to destroying entire planets was considered just enough to permanently destroy him.