Harken all well to this story of great ambition thwarted and subverted by the machinations of the Dark and Ruinous Power of the Lord of Pleasure. Let the story of what occurred on the planet of BARDOS be a warning to all those who knowledge seek, and remember always what the Emperor your saviour tells thee; that knowledge holds great power, and man should not seek it out.
Our story begins, as so many do, with simple human ambition. The Mykene Warriors were a noble and prosperous successor chapter to the Ultramarines, who daily venerated the Imperial Creed and who adhered most strongly to the Codex. Their greatest victory was sealing the forces of a mighty daemon deep within a lost island in the midst of a storm-tossed ocean on a planet far from civilisation and the light of the Emperor. This crusade, fought centuries ago not long after the chapter’s inception, was held in myth by the people of the Imperium who came to live around that world – BARDOS. Bardos in time became also prosperous, also loyal, with the Mykene Warriors watching over them – for in his great wisdom, The Emperor deigned to appear to the Mykene Warriors’ chief Librarian and Master of the Forge, Tristan and Ju’zar, He claimed that Bardos was forever theirs to protect, and that they should recruit their novitiate from there.
News that a Space Marine had seen the Emperor in a vision troubled the Witch Hunters most sore, and one more radical of their number, the Inquisitor Isolde, called for a crusade against the heretic Tristan. It greatly pained all men of reason and faith to see battle-brother fighting Imperialsoldier, but nevertheless the battle did rage over Bardos and in time came back upon that island where the demon had been sealed.
Chaos is itself a deadly, treacherous thing, and none are safe from it. The Inquisitor Isolde was not immune to the demon’s blandishments and so in time her host was drawn to the island. Tristan saw what was fated to happen and in order to prove his piety rushed his own host there – the Mykene Warriors’ First Company – to stop Isolde or reseal the demon. He was too late. The demon was already released, and waiting for him with the Inquisitor its vessel. Being as it was a capricious creature, it enslaved Tristan, playing a cruel jest on him. Isolde’s mind was cast into a book, and the demon now possessed the mightier Librarian over the comparatively feeble Inquisitor – the result was now corrupted and mutated far beyond recognition into Acheron, a Sorcerer of Chaos. With all of Tristan’s psychic arts, and the ruthlessness of an Inquisitor formerly renowned for piety and crusading zeal, the Sorcerer Acheron became the voice of the demon. It is inaccurate to claim Acheron has any human aspect left; it never removes its armour and many suspect the armour is empty, or that Acheron is so mutated that it is not even human except in having two legs and two arms.
Yet that was not the only outrage to be visited upon the Mykene Warriors by the demon. The Mykene Warriors’ chapter-master became the bodily incarnation of the demon, taking the name of Imperator Magnum Tenebrarum. The Master of the Forge turned his energies from maintaining holy wargear to creating vile demon engines with the plans provided by the demon; he is now known only as the Infernal Doctor Ju’zan, whose insane creations roar up from that isle on Bardos to march alongside the hosts of the Imperator and Acheron.
Bardos itself has become a mockery of the paragon of an Imperial World it once was, now only a spawning ground and training-field for the corrupt and decadent warriors of the Mykene Legion. The Lord of Pleasure has had his way with them, but not in his usual grotesque fashion; indeed, they eschew mutation. Instead, they strive only for perfection – they have been wronged by the Inquisition, and it was the meddling of an Inquisitor who unsealed the Imperator, As a result, the Imperium is anathema to them; it represents a status quo that is unthinking and intractable and must be purged one battle at a time.
When the Mykene Legion go to war, only rarely does the Great General himself take to the field; he delegates to Ju’zan or Acheron almost always. They make extensive use of cultists tithed from the population, many still using the tattered uniforms of the Guard regiments sent in Isolde’s crusade force, They also make heavy use of demon engines; Ju’zan has a great mechanical beast army at his command, yet he is most protective of it, sending only a few out at a time. This caution is perhaps a holdover from the Codex Astartes’ tracts on economical use of force, for the Legion fight much like a loyalist chapter. Indeed, while the demon who caused their fall was one of the Lord of Pleasure, they have also embraced the Lord of Decay deeply; their veterans have become the Iron Army, corroded and antique Space Marines who are intractable and almost inured to pain. This tenacity can only be supernaturally aided.