The Imperial Fists are one of the First Founding Chapters of the Space Marines and were originally the VII Legion of the Legiones Astartes raised by the Emperor Himself from across Terra during the Unification Wars.
The Imperial Fists stand out from other Space Marine Chapters since they possess no fixed homeworld, although they are most frequently based on Terra. Instead, the Imperial Fists rely on their 10,000-year-old mobile space fortress, Phalanx, to serve as their fortress-monastery.
They maintain recruitment-chapels on various worlds spread throughout the Imperium. Part of the Imperial Fists' duties during the Great Crusade were to function as the Emperor's "personal praetorians," accompanying Him everywhere.
The Imperial Fists were usually used to strike a decisive blow against the enemies He confronted during that time. The role of the Emperor's bodyguards since he was mortally wounded during the Horus Heresy and interred within the Golden Throne at the heart of the Imperial Palace on Terra has now been entirely taken over by the Adeptus Custodes. But the Emperor's ancient trust remains a potent honour for the Imperial Fists and their Successor Chapters in the present day.
The Imperial Fists are the inheritors of the proud traditions of Primarch Rogal Dorn, his name venerated by countless trillions across the Imperium. History does not clearly record the details of the world on which the infant Dorn was cast when the primarchs were scattered to the corners of the galaxy. What is known is that he presented himself to
the Emperor as the Great Crusade reached the Ice Hives of Inwit, offering one of the mightiest space-going vessels ever constructed by Humans during the Dark Age of Technology as a sign of his fealty.
The Emperor welcomed His long-lost son into the ranks of the primarchs and granted him primacy over the Imperial Fists Legion. The Master of Mankind returned Dorn's vessel -- called Phalanx -- to the primarch, and it became the base from which Dorn, and sometimes the Emperor Himself, commanded some of the most glorious campaigns of the Great Crusade.
Dorn and his Legion proved the masters of every aspect of warfare, but in particular the Imperial Fists excelled at siege craft, whether on the attack or the defence. This propelled them into a bitter rivalry with the Iron Warriors Legion and their jealous primarch Perturabo, the flames of which were wantonly fanned by Fulgrim, the primarch of the Emperor's Children Legion.
Fulgrim is said to have asked Dorn if a fortification of his design could withstand an assault by the Iron Warriors, and Dorn is said to have answered that it could. Perturabo took the answer as a boastful sleight, and the seeds of a hatred that would only grow more bitter as the Terran millennia passed were sown.
Loyalty in time of betrayal was not easy to measure, for one cannot look at the face of an ally and know if he is truly a friend or an enemy. Even after Horus' treachery was made manifest upon the plains of Isstvan III and the Drop Site Massacre of Isstvan V, the truth of who was Traitor and who remained loyal was far from clear.
In this age of betrayal, one Legion stood as a pillar of loyalty amongst the sea of doubt. The Imperial Fists and Rogal Dorn, ever true, never swerving from the toll demanded by a war of brothers, bore the weight of loyalty without breaking, but not without cost. Sacrifice without limit changed those who survived.
As fate would have it, Dorn's prediction was put tragically to the test when, at the height of the Siege of Terra, the fortifications he had added to the Imperial Palace were sorely tested by the Traitor Legions. Though the World Eaters are said to have forced a breach, by sheer bloody savagery rather than any genuine skill at the siegemaster's craft, the Warmaster Horus fell in combat to the Emperor before the matter could be truly decided.