Hasophet was a Sorcerer and the Magister of the Mind-Eaters thrallband of the Thousand Sons Traitor Legion. Hasophet believed he had received a vision from Tzeentch, the Chaos God of Change, that promised that he would eventually ascend to daemonhood if he completed nine hundred and ninety-nine special rites that would further the Architect of Fate's plans in the mortal realm.
But Tzeentch's schemes are rarely straightforward or completely understood, even by his most devoted servants. After almost 10,000 Terran years of carrying out each of his appointed tasks, Hasophet and his warband suffered a fate very different from the one they had hoped for -- but one still pleasing to their ever-scheming patron.
Omen of Omniscience
At an unknown time during the 32nd Millennium, Hasophet, the Magister of the Mind-Eaters thrallband, received a vision of his Tzeentch-ordained destiny. He saw a time in his future when he will devour the thoughts and memories of an entire world, and in doing so will achieve apotheosis. The Mind-Eaters embarked at his direction on the first of nine hundred and ninety-nine rites that will lead to this portended moment.
The Shrouded Crystal
Nearly ten thousand Terran years later in the late 41st Millennium, an endless psychic scream lured Vasellisk the Shrouded, a Sorcerer warlord of the Night Lords, to the obsidian mines on the world of Xanthematos. As his warband set about butchering the Imperial work crews, the terror of those slain continued to linger in the form of disembodied Warp-gheists. The sight of spectral figures crowding the mines and howling with fear blinded Vasellisk to the true sorcery at play, for the scream from the planet had been emitted because the world had been hex-bound by Hasophet and his Mind-Eaters.
As Vasellisk revelled in the resonant terror, the Mind-Eaters sealed the mines with the Night Lords inside. In the final twist of Hasophet's curse, the spirits of the dead burst into Warpfire, filling the subterranean tunnels with screaming flame. By the time the mines were reopened, every last Night Lord had been reduced to ash -- all except for Vasellisk the Shrouded, whose body had been melted into a lump of dark glass. This Shrouded Crystal was the foreseen prize of Hasophet's seven hundred and sixty-fifth rite, and it pulsed with the psychic energy of the Sorcerer it once was.
Wages of Change
Next, after undermining the millennium-long battle plan of Korthuphos -- an Exalted Sorcerer of the Cult of Magic -- Hasophet was challenged to a psychic duel by his fellow Thousand Sons magus. As the two locked minds in combat it was soon made clear that Korthuphos was the more powerful psyker, but Hasophet unsheathed the Dagger of Reflections, acquired centuries before during his eighty-seventh rite.
The mind-flames cast out by Korthuphos were drawn towards the shimmering dagger before being forced back in a thunderous wave, pulverising the brain matter of the Exalted Sorcerer. Korthuphos began to slump over with liquid oozing from his helm, but before he hit the ground Hasophet plunged the ensorcelled dagger into his fallen opponent's chest, carving out his still-beating hearts. These were the trophies of his eight hundred and twenty-eighth rite.
The Psychophage of Mangel III
Finally, Hasophet and his Mind-Eaters descended upon the Imperial Hive World of Mangel III amidst an ongoing T'au invasion. Before landing the Sorcerer shattered the Shrouded Crystal in orbit, casting its shards throughout the atmosphere to summon an impenetrable darkness which surrounded the planet. Cut off from orbital reinforcements and relays, the T'au armies and Imperial Planetary Defence Forces continued fighting in utter confusion.
In the Valley of Sacrifice, between the lines of the battling armies, the Mind-Eaters arrayed the trophies and fetishes acquired from their nine hundred and ninety-eight preceding rites in a great crescent, and between the horns of the crescent Hasophet mounted an enormous pyre. From its pinnacle he beheld the encroaching T'au and Imperial forces -- they were to be his, their thoughts and memories devoured as had been foretold nearly ten thousand years before.
Holding aloft the hearts of Korthuphos, Hasophet ignited his pyre with their blood, incanting an oath to Tzeentch as the flames begin to lap his armour. The sudden rush of psychic energy toward Hasophet shredded the minds of the hundreds of thousands of combatants on Mangel III, siphoning their very life force into the Sorcerer. But as the Grand Conspirator's changes took hold Hasophet screamed in agony.
The armies on the horizon were pulled physically towards him like gnats caught in a thundering vortex. Ranks of screaming bodies and enormous war engines flew across the darkened land, colliding with Hasophet where they were quickly absorbed by his warping form. His body devoured metal and flesh with equal voraciousness as it continued to grow, howling in excruciation from newly forming maws. His mass pupated, not into the form of a Daemon Prince as he expected, but to that of a Mutalith Vortex Beast.
The Warp vortex emanating from the hideous creature extended outward with each newly consumed sacrifice until it encircled the entire planet, and with a final mind-tearing scream Mangel III itself was torn from realspace to become Tzeentch's newest Daemon World. In its place there was left only a perpetual dark shroud and an echo of Hasophet's final, pitiful cry.
- Codex Heretic Astartes - Thousand Sons (8th Edition), pp. 28-31