Tzeentch - Tzeentch and the Thousand Sons: The Thousand Sons Traitor Legion of Heretic Astartes serves Tzeentch exclusively. They were once the XVth Legion of Space Marines founded on Terra, created in the late 30th Millennium to reclaim the stars for Humanity after the horrors of the Age of Strife. For some time, they fought with distinction and were nearly indistinguishable from the other Space Marine Legions. Shortly into the Great Crusade, however, the Thousand Sons began to change.Many manifested psychic abilities; others underwent a "flesh change" and developed rapid and uncontrolled physical mutations. Mutated battle-brothers were placed in stasis to await an eventual cure, and the ranks of the Thousand Sons grew thin. Leaders of the Imperium became concerned and many argued that the Legion should be disbanded and all traces of its existence removed from Imperial history.The Great Crusade wore on and the forces of the Emperor  eventually reached the planet Prospero, where they discovered Magnus the Red, the cyclopean primarch of the Thousand Sons. Once introduced to the XVth Legion created from his genome, Magnus acted swiftly to save his progeny, almost all of whom had succumbed to the flesh change. Through some unknown and possibly arcane process of sorcery gained through interaction with the entities of the Warp, a bargain that cost him one of his eyes, Magnus stabilised the Thousand Sons' gene-seed, but by then, the numbers of the Thousand Sons were small indeed.Under Magnus' guidance, the Thousands Sons rebuilt their Legion, recruited new battle-brothers from the population of Prospero, and reorganised themselves. They developed the most powerful Librarians of that era of Imperial history as well as unconventional tactics that involved sorcery and diplomatic trickery.This ended with the Council of Nikaea and the Emperor's decree to abolish the use of sorcery and other psychic powers in the Imperium and amongst the Space Marine Legions, as well as the tragic and terrible events that led the Thousand Sons to turn their back on the Imperium forever.At the start of the Horus Heresy in the early 31st Millennium, Magnus the Red tried to warn the Emperor of Horus' treachery by using sorcery to reach across the vast interstellar distances between the Thousand Sons' homeworld of Prospero and Terra, but the Emperor rejected the sorcerous warning as a deception perpetrated by Chaos against his beloved son Horus.He sent Leman Russ, the Space Wolves  Legion's primarch, along with his Legion and elements of the Sisters of Silence and the Legio Custodes to bring Magnus back to Terra for trial for violation of the Council of Nikaea's proscription on the use of sorcery, but Russ' orders were maliciously modified by Horus to get the Space Wolves to attack the Thousand Sons outright instead and force them to turn to Chaos to save themselves.Russ attacked and ultimately, the XVth Legion's homeworld burned during the terrible campaign remembered as the Fall of Prospero. Some of the Thousand Sons, including Magnus the Red, managed to escape with the help of their new patron, Tzeentch, and sided with Horus against the Emperor to seek vengeance for all that had been lost on Prospero.They became Traitor Marines and fought alongside the Warmaster Horus and his forces in the failed attempt to overthrow the Emperor and His servants. Now and forever aligned with the Changer of Ways, the Thousand Sons use their powers to pursue knowledge and glory for themselves and their patron god.After embracing Tzeentch, the Thousand Sons continued to develop their combat doctrine of guile and trickery, and they continued to favour ranged weapons and sorcery over close combat. They changed their Legions' colours from crimson to blue and gold, the favoured colours of the Changer of Ways, and added elaborate headdresses to their helmets.The flesh change, which had been held in check by Magnus' intervention, began to take hold once again due to their exposure to the power of the Warp within the Eye of Terror where they had taken refuge on the Daemon World known as Sortiarius, the Planet of the Sorcerers, and many of the Thousand Sons experienced radical mutations. The machinations of Ahriman, the Chief Librarian of the Thousand Sons and Magnus' second-in-command, led to the horrific spell known as the Rubric of Ahriman, which permanently solved the issue, though not in the way the sorcerer had expected.Ahriman's horrifying Rubric did prevent further mutations in those of his brethren possessed of psychic abilities and adept at sorcery, but forever changed his other, non-psychic brothers into dust, their souls forever encased in their ensorcelled suits of power armour, transforming them into undead Rubric Marines.The Thousand Sons who did possess psychic powers found these abilities greatly enhanced and now lead their phantom battle-brothers into war against the Imperium of Man and the Corpse Emperor they believe betrayed them so long ago.Upon learning of the failure of the Rubric, Magnus in his rage banished Ahriman from the Planet of the Sorcerers. This was the first of many schisms that split the Thousand Sons, divisions that eventually caused estrangement from their own primarch.As a result of this internal strife, the Thousand Sons effectively no longer function as a true Legion. Instead, they fight as isolated warbands and individual warriors. Some serve Tzeentch devoutly, others begrudgingly, and others as mindless conduits for the devastating sorcerous power of the Warp.