Death Guard - The Doom of the Death Guard: During the subsequent assault on Terra itself, the Death Guard were part of Horus' invasion force. However, en route, the entire Death Guard Fleet became trapped in the Immaterium due to the actions of First Captain Calas Typhon, trapping them in a perpetual nightmare.It was whilst on campaign with the Word Bearers Legion earlier in the Great Crusade that Typhon had learned of a different path for the Legiones Astartes to follow, a future where his hard-won but hidden psychic abilities would be a source of greatness instead of a taboo to be hidden from sight.The foremost Chaplain of the Word Bearers, Erebus, inducted Typhon into the secrets of the Seven Pillared Lodge, one of the Warrior Lodges based on the beliefs of the feral peoples of Davin that had begun to spread throughout the Space Marine Legions in the later days of the Great Crusade. It was during this time that Typhon caught a glimpse of what the Space Marines could truly become if they shrugged off the yoke of the Emperor's ambitions.Perhaps Typhon's revelation was instrumental in Mortarion's own fall to the Ruinous Powers; perhaps Mortarion would have walked a dark path on his own. Either way, the troubled Death Guard Primarch saw a worthy master in Horus, whereas in the Emperor he saw only a self-serving and pompous pretender who had stolen Mortarion's hard-won kingship over Barbarus in a single solar day.As the Heresy that Horus initiated slowly but surely escalated into a galactic civil war, Mortarion ordered his fleet to head for Terra with all haste, intending for the Death Guard to join the other Traitor Legions in the destruction of the False Emperor. By this point, Calas Typhon served one master alone, and it was not his Primarch.Typhon had seen to it that the fleet's Navigators were killed to a man after concocting a tale that they were traitors who had been receiving messages from Malcador the Sigillite, but reassured Mortarion that the psychic abilities he possessed would see them through their journey in the Empyrean safe enough.Though he hated the concept of relying on witchery, Mortarion was left with little choice. The Death Guard fleet made transition into the Warp, and in the process damned themselves to an eternity of war as the puppets of a foul and ancient god.In leading the Death Guard into the Warp, Typhon had delivered them into the clutches of his new master, Nurgle, the Lord of Decay. The strange tides of the Empyrean are notoriously fickle, and during their voyage the entire Death Guard fleet was becalmed. As their warships lingered, directionless and without hope, the cloying influence of Father Nurgle began to take hold.The Death Guard were subjected to the terrible infection of the Destroyer Plague and Nurgle's Rot, as Nurgle's power managed to infiltrate the vessels of the XIVth Legion. It polluted the mechanisms of the vessels themselves as easily as it did the transhuman warriors within. Before long, fat devil-flies buzzed through the thickening miasma inside each warship. Where they bit at the desperate warriors trapped within, flesh turned to suppurating jelly.The daemon-venom of their stings caused flesh to blossom into hard new growths. Bellies distended and eyes ran like cracked eggs; even Power Armour melded and flowed into strange new shapes. Here, the superhuman resilience of the Death Guard proved their enemy, for they could not simply die.Instead, they were slowly, sickeningly transformed into Plague Marines, their souls claimed by Nurgle in exchange for a permanent release from their pain and suffering. Typhon, having orchestrated this grand corruption, was rewarded most of all.Swelling in size, his skin and armour became one. Great funnels of pestilential bone burst from his body. Into these poured thousands of Nurgle's daemon-flies, gnawing him from the inside out until his rotten shell teemed and heaved with squirming life. Typhon became a great hollow colony of disease-carrying insects. The bone funnels that sprouted from his back coughed black decay as Nurgle's servants regurgitated the psychic energies pulsing through what was left of his herald's body.Typhus, Chaos Lord and Host of the Destroyer Hive, had been born, most blessed and most cursed of all his repugnant kin. Since that bygone era, Typhus has visited a hundred thousand diseases upon the Imperium of Man. The Destroyer Plague is without doubt the most virulent of all, though fortunately its vector of daemonic insects means that it is of limited use when infecting entire star systems.There was nothing so terrifying to Mortarion and the Space Marines of the Death Guard than watching the plague render their legendary resilience meaningless. The pestilence raced through the entire fleet, roiling in their guts, bloating and distending their superhuman bodies, transforming them into horrible, pustulent grotesques.They were made corrupt within and sickening to behold without. They grew sicker by the solar minute, their incredible transhuman constitution their worst enemy as their bodies refused to die and they were wracked with the agony of their macabre transformation. What they endured was unimaginable, and none suffered worse than Mortarion. Whether he perceived in those terrible hours the loss of what he had once stood for, and the damnation he had wrought upon himself and his Legion, only Mortarion will ever know.Unable to endure any longer, Mortarion offered his soul and those of all his sons to the Immaterium in exchange for deliverance from eternity trapped within the twisting corridors of Warpspace in constant, unendurable pain. A presence answered, as though it had been waiting all along. In the depths of the Warp the great god Nurgle, Lord of Decay and Father of Disease, claimed the Death Guard for his own.What emerged from the Warp when the Death Guard fleet broke out into realspace bore little resemblance to that which had entered. The gleaming ivory armour and jade heraldry of the once-proud Imperial champions was no more, in its stead was a sickly pall of greenish hue. Bloated and corpulence replaced the sleek proud form of the Death Guard Astartes as every warrior was now pock-marked with boils, scabs and putrescent sores. Maggots writhed in their unhealing wounds and the air about them was clouded with swarming bloated black flies. They bore the foul stink of corruption.Even their weapons and war machines had been mutated and were now powered by the sickly sorcery of the Plague God, glowing with lambent green Warp energy and oozing gangrenous pus. The Death Guard were now walking pestilence carriers; they had become the first Plague Marines.Mortarion himself was also changed, growing taller and more gaunt, as if stretched on a rack. In return for rescue from the torments of the daemonic plague, Nurgle had set him on the path to daemonhood and transformed Mortarion into Nurgle's greatest daemonic servant: the Prince of Decay, the very image of death. Condemned to a deathless state of decay, the Death Guard would spread their pestilent diseases the length and breadth of the galaxy for the greater glory of Chaos.In the end, Horus was ultimately defeated by the Emperor and cast down during the Siege of Terra, but unlike the other Legions, who splintered and fled into the Eye of Terror, Mortarion's Legion made an orderly withdrawal, force after force breaking themselves on the superating warriors of the Death Guard.Mortarion led his forces, in an ordered formation, back into the Eye of Terror. Mortarion claimed the Daemon World known as the Plague Planet as his new homeworld and it proved to be an ideal base for launching attacks from out of the Eye into the physical universe.He shaped it so well that Nurgle soon promoted him to become the greatest of his Daemon Princes. Mortarion had finally gotten what he wanted, a world of his own. He ruled over a toxic Death World of poison, horror and misery. But for better or worse, the Death Lord had come home.Some of Mortarion's sons embraced their new form, believing in their arrogance that they had passed through the eye of the needle and proved themselves the only mortals worthy of Nurgle's patronage. Others hated the plague that had laid them low, the weakness it implied; for these warriors, nothing would suffice but to spread ruin and sickness until the entire galaxy was brought down to their level.Others still were driven quite mad, taking on aspects of rambunctious glee or morose, entropic misery. Whatever the case, the Death Guard had become Nurgle's servants, body and soul, forevermore. In the millennia of war that followed, their devotion to their rancid deity would only deepen further.