Solun Decius was a Space Marine of the Death Guard Legion during the Great Crusade and the opening days of the Horus Heresy in the late 30th and early 31st Millennia. Decius was the youngest member to have served in the Command Squad of the 7th Great Company of that Legion which was led by Battle-Captain Nathaniel Garro.
Following the events of the Istvaan III Atrocity, Decius fled with his commander aboard the frigate Eisenstein to bring word of Horus' treachery to the Emperor on Terra. While travelling through the Warp, Decius was gravely wounded when he fought against the reanimated corpses of his traitorous brethren, the first Plague Marines of Nurgle, and was infected with Nurgle's Rot.
Arriving at Luna, Garro and his fellow Loyalists were confined within the formidable Somnus Citadel under the watchful eyes of the Sisters of Silence. While recovering within the citadel's Apothecarion, Decius succumbed to the effects of the vile disease that ravaged his body, and he became a willing servant of Nurgle in return for an escape from his constant pain.
The Plague God transformed Decius into the daemonhost of the daemonic entity known as the "Lord of the Flies." This foul creature was confronted by Battle-Captain Garro and was defeated, its black soul cast back into the Immaterium from whence it came.
The Lord of Flies would return to plague Garro and his Knights-Errant again on Terra in the days just before the final battle of the Horus Heresy, though it would possess several more Space Marine hosts before being defeated once more by Malcador the Sigillite on the slopes of the White Mountain, a large installation protected against psykers on Terra's surface.
Solun Decius was a member of the 7th Great Company commanded by Battle Captain Nathaniel Garro, and was the youngest member of Captain Garro's Command Squad. Brother Decius remained loyal to Garro, despite the corruption that had begun to creep into the Space Marine Legions under the Warmaster Horus' command, in the form of the warrior lodges.
Garro expressed his disapproval of the secretive lodges and as a result Decius chose not to join the warrior lodge that already existed within the Death Guard when offered membership. During the outset of the Istvaan Campaign, Garro's 7th Great Company fought in concert with the Emperor's Children's elite 1st Company against traitorous forces on the world of Istvaan Extremis, the outermost planet within the Istvaan System.
Whilst fighting against a powerful Slaaneshi psyker known as a Warsinger, Decius' life was saved when Garro pushed the young Legionary out of the way of its psychic attack, which badly wounded the Battle-Captain. Though gravely injured, Garro continued to fight on, fighting back-to-back amidst the rising tide of enemies until the battle was successfully concluded.
As a part of Garro's Command Squad, Decius was fated to be aboard the frigate Eisenstein during the Istvaan III Atrocity, when his commander took control of the vessel and fled the Istvaan System through the Warp in an attempt to bring word of Horus' betrayal to Terra.
En route to the Throneworld, Decius and a number of his fellow Loyalist Death Guard fought a battle against the reanimated corpses of their former traitorous comrades aboard the vessel, who had become the first Plague Marines of Nurgle when the Plague God's influence had insinuated itself through the damaged Eisenstein 's Gellar Field while the vessel was travelling through the Empyrean.
Decius was grievously injured when he was stabbed by one of the Plague Marine's Plague Knives and in a vain attempt to halt the advance of the supernatural corruption caused by that Chaos artefact, he bravely cut off his own arm. The severely wounded Astartes was then taken to the Apothecarion and put under the care of Apothecary Meric Voyen, but there was no cure available in the entire corpus of Imperial medical science that could ease Decius' suffering.
After completing their arduous journey and delivering their message to the Emperor's acting Regent, Malcador the Sigillite, Garro and his men were placed under house arrest and held in solitary confinement in the Somnus Citadel on Luna, under the watchful eyes of the Silent Sisterhood. Their fate was yet to be decided.
In the meantime, the mortally wounded Decius finally lost his fight to the supernatural disease later known as Nurgle's Rot that ran rampant throughout his rotting, corpulent form. Giving himself over fully to the offer of Nurgle to end his pain, Decius' body was possessed by and metamorphosed into the mutated form of the daemonic entity known as the "Lord of the Flies."
His twisted body took on a daemonic appearance: it possessed an arachnid-like head with numerous eyes and mandibles in place of his mouth, while his decapitated arm grew grotesquely into a great skeletal hand similar to a Power Fist.
The Lord of Flies proceeded to wreak havoc inside the fortress, killing two of his former comrades before Captain Garro strode forth and slew the monstrosity outside the fortress on Luna's barren, airless surface, casting the Lord of Flies' daemonic spirit back into the Warp from whence it came.
Almost nine standard years later, in the final days of the Horus Heresy, just before the start of the Battle of Terra, the Lord of Flies assaulted the mobile industrial platform known as the Walking City on Terra. The daemon appeared as a massive horde of plague flies that infected the people of the Walking City and transformed them into fly-infested zombies. The Knights-Errant were sent to defeat the creature, one of many such Chaos assaults which occurred in the days just before the start of the Siege of Terra.
During the battle, the Lord of Flies used the voice of Solun Decius to goad the leader of the Knights-Errant, Nathaniel Garro, promising him that all his efforts to stop Chaos would be in vain and offering him the chance to rejoin his fellow Death Guard in service to Nurgle. Decius' voice admitted that he had been consumed by a daemon known as the Lord of Flies and that was really all that was left of him. The Knights-Errant succeeded in cleansing the Chaos taint from the Walking City, though the Lord of Flies promised he would yet be the death of Garro.
Later, a force of Chaos Cultists struck at the White Mountain, a secret subterranean installation on Terra that was heavily protected against psychic intrusion. The facility was being used to research what had happened to a group of Sisters of Silence who had been captured by the forces of Chaos during the Heresy and then recovered by the Loyalists. In the course of the assault, the Knights-Errant under Garro's command once more moved to defend the facility, and were attacked by the Lord of Flies.
During the combat, the daemon revealed that after it had been defeated by Garro upon Luna, it had possessed the body of Meric Voyen, the Apothecary of The Seventy who had once tried to save Solun Decius upon the Eisenstein after his infection. Voyen had been among the 70 Death Guard Astartes who remained loyal after the Eisenstein arrived at Terra. The daemon laughed as Garro realised that he was once again forced to kill the body of a man who had once been a friend.
Garro destroyed the Voyen host body, but the daemon then moved to possess the Knight-Errant and former World Eater Macer Varren, who had been mortally wounded during the battle for the White Mountain. Varren assaulted his comrades, but froze when his fellow Knight-Errant Garviel Loken confronted him and tried to remind him of their friendship. Varren's soul regained enough control over his own body to grab a belt of grenades from Loken's armour and set them off. Varren chose to destroy himself rather than let the daemon continue to control him.
Free of flesh once more, the daemon began to hunt for another host, but Malcador the Sigillite finally entered the battle upon the White Mountain's slopes and unleashed his full psychic might against the creature, blasting it to ash. However, the Sigillite warned the Knights-Errant that like all daemons, the Lord of Flies could not be completely destroyed while in realspace, and would reform within the Warp.
Mephitic Perdition of Flies
When Solun Decius was stabbed by a Plague Knife and infected with Nurgle's Rot, he attempted to stem the corruption by cutting off his own arm which was encased within a Power Fist.
This archaic Chaos relic was now known as the Mephitic Perdition of Flies, and though still a potent and formidable weapon, it was corrupted with the malefic power of Nurgle.
- The Flight of the Eisenstein (Novel) by James Swallow
- Dawn of War II - Chaos Rising (PC Game)
- The Buried Dagger (Novel) by James Swallow, Chs. 1-6