The ivth.
Once a company of iron warriors subduing and drawing various worlds into the fold of what they envisioned as mankinds grandiose empire. Hoping someday to ply their skills as builders in creating wonders. After losing many of their most promising architects engineers in thankless and forgotten in this war. Innumerable battles who’s necessity was valid but costly and terrible, they became disenchanted. No other legion possessed the temerity of the ivth. Instead tales were spun to place the consistently late comers and glory hogs the imperial fists as great conquerors! Over time they saw the appparent lack of effort on the part of other legions to do what had to be done as contempt for the ivth. It created a deep rooted bitterness. With each siege, they would send more and more solar auxiliaries to die the death of a mere mine detector or simply to exhaust enemy storesof munitions. “Corpse grinders” the moniker did not bother the ivth, death is just a part of the war they had to fight for the betterment of humanity. Why not have humanity pay the blood price for once? It is better to pay for it in human rather than astartes blood.
Then it happened, the emperor grew tired of his tools. He tasked the ivth with the impossible task of exterminating the hrudd. Xenos creatures capable of distorting reality in a way with what would be later known as “entropic fields.” History is known, despite fighting a terrible battle even so serious as to have the lord of iron take a personal interest in and resulted in the loss of that world along with the demotion and ousting of Dantioch a respect Ironwarrior!
Now Olympia openly rebels from the comfort that was provided on the deaths of countless astartes! How dare they! Bringing swing discipline perturabo granted the ivth decimation! And took to it with glee. Until perturabo felt remorse for what he apparently saw as despoiling his home-world and demanded the ivth stop, hang their heads in shame and leave the imperium to seek refugee with his beloved brothers lead by then warmaster, horus.
The dream died.
With contempt for the imperium they helped to create, the ironwarriors take great joy in turning the very tools and skills they utilized in the creation of the imperium during the great crusades upon the imperium. An empire which took the blood, sweat and lives of countless Legiones Astartes for granted, unsung forgtten and dust upon countless worlds. 10,000 years later they still stew in anger as the imperial citizen sit in the comparatively lavish comfort they provided! Despite the satisfaction of the “ironcage,” it felt hollow! They needed more vengeance. It became an obsession. The systematic destruction of imperial worlds, fleets and armies was the only thing that abated the hatred and bitterness. This obsession would catch the attention of slaanesh. Xenos, human, post human, all would be torn apart with the cold savagery that only the ivth were capable with. Plying their mathematical minds to each battle and leaving to seek new targets for their anger elsewhere after each battle.
The imperium would know the great and terrible force of the IVth!
Few of the iv are the proud olympian warriors which set out to shape the imperium in their noble conquest, may great artisans perished without ever helping build the great cathedrals and stoneworks they had planned, they were never given the opportunity. Now built from various malcontents, they scour and strip each world they conquer, seeking various prizes. Killing millions over merely blocking a supply route or rumored technological items to bring to their dark mechanum allies to strip apart for the knowledge in exchange for the production off either mk3 armor or weaponry from the time before what imperials call the “Horus Heresy.”
Retribution! Vengeance. These imperials had no strength, will, faith or honor. Bring the iron to them!
Among them, one warsmith took such great joy in inflicting savage retribution, his name was forgotten millenia ago but is merely know as slordag, a daemon prince who revels in the misguided martial pride of those inducted with the ivth and the systematic torture of citizens. He has a tallent for drawing out suffering. Something that has only become what some would consider supernatural. His sick pride and madness extend to those beneath his command.
A madness he has spent shaping into a cold an bitter cruelty among his warband. This has even been nurtured among the imperials who swore allegiance to the ivth. Even recruiting several dark mechanum looking to ply the flesh from the living in sweeping advances these scavengers travel along with with the ivth.