The history of the Black Templars can be traced back to the Imperial Fists defense of the Emperor's Palace during the Horus Heresy. After the Traitor Legions had been defeated it was decided that the loyal Space Marines should be split into smaller chapters. Rogal Dorn, Primarch of the Imperial Fists, reluctantly agreed and so the Black Templars were created. Since this time the Black Templars have been on the greatest and longest crusade the Imperium of Man has ever known to prove their loyalty to the Emperor.

    At the birth of the Imperium, during the Great Crusade and when the Emperor walked among men, the mighty Warmaster Horus was seduced by the Dark Powers of the Warp and declared himself rightful ruler of mankind. Along with Horus, nearly half the space marine legions revolted against the Empeor's leadership, and from their rank arose warriors who were so wholly devoted to their gods that they became Champions of Chaos. Even as Horus' forces assaulted the Imperial palace at the end of the Heresy, Rogal Dorn chose a warrior from the ranks of his Imperial Fists to be the first Emperor's Champion. Brother Sigismund, finest of the warriors of Terra, was given the best armour and weapons and swore a holy duty to seek out the Champions of Chaos and slay them. And so he did, counting fully two dozen of the warped creatures in his bloody tally before Horus was defeated and the Traitor Legions fled into the Eye of Terror.

    At the end of the Heresy, the Primarch Roboute Guilleman of the Ultramarines Legion devised a military organisation that would spread the power of the Legion Astartes, Imperial Navy and Imperial Guard across the galaxy, so no longer would one individual weild the power of a Legion again. For the Space Marines, these rules were laid down in the Codex: Astartes, a mighty tome that also dealt with unit organisation, markiong tactical doctrine and all other aspects of the Marines' structure. Rogal Dorn, Primarch of the Imperial Fists, responsible for the defense of Terra itself, refused to have his legion broken down into smaller chapters, stating that it was his sacred duty to protect the Emperor and he could not afford to split his forces across the Imperium. Dorn called Guilleman a coward, for his legion had not participated in the defense of the Imperial Palace, while the Ultramarines' Primarch accused Dorn of being a rebel and a heretic for refusing the dictates within his Codex: Astartes.

Dorn would not relent, and neither would Guilleman. Leman Russ of the Space Wolves and Vulkan of the Salamders agreed with Dorn for they too did not want their legions scattered to the corners of the Galaxy, but Ferrus Mannus, Primarch of the Iron Hands and Corax of the Raven Guard backed the Ultramarines. In the gulf left after the near-death of the Emperor, it seemed the Space Marines were destined to tear themselves apart. When the Imperial Fists began to be violently persecuted for their supposed heresies, and the strike cruiser Terrible Angel was fired upon by the Imperial Navy, it was almost inevitable that once more internecine war would engulf the Space Marines and the Imperium. But even as the newly formed Chapters and the old Legions were preparing for battle, Dorn relented. he agreed to the formation of two new Chapters form his legion- the Crimson Fists and the Black Templars. He chose Sigismund to lead the Black Templars and the Cpater took upon themselves the black and white panoply of his armour.

    Sigismund had bben chosed as the Emperor's Champion for his fervent faith in the Emperor and his undying devotion to mankind. Seeing the strife that currently beset the Legions, he determined that a gestureof supreme faith was needed. As High Marshall of the Black Templars, Sigismund declared that after leaving Terra, he would prove his loyalty, never resting in the prosecution of the enemies of the Emperor. It is an oath that every subsequent High Marshall has renewed, and so the greatest and longest Crusade was begun. it has continued unbroken for ten thousand years.

    The Black Templars have no single homeworld, instead they are a fleet based chapter. The Black Templars establish Chapter keeps on every world they conquer or reclaim for the Emperor. The main purpose of the Chapter keeps is to maintain recruiting, and act as staging posts for the crusades. The High Marshall himself, currently High Marshall Helbrect, has his own battle barge, the Eternal Crusader (funnily enough), so he can travel from crusade to crusade, lending his considerable fighting prowess and tactical genius. The Eternal Crusader is huge, even by battle barge standards, having being extensively refitted and expanded over the millenia. It has copious room for extra docking facilities and launch bays, as well as room for twice as many space marines than a standard battle barge.

    The Black Templars have continued in the style of their founder, Sigismund, in preferring close combat to ranged warfare. This is further emphasised by the fanaticism of Black Templar battle brothers, whose righteous anger makes them impatient and headstrong. They will drive towards the enemy relentlessly, their own casualties only serving to spur them on faster, hungry for vengeance on the slayers of their brethren.

    As part of their devotion to the emperor, the Black Templars swear life oaths of faith and protection. Before a battle, it is customary to renew one of these vows to the Emperor, the type of vow made focusing the thoughts of the initiates on a particular aspect of their duties, encouraging bravery, ruthlessness, or sacred revulsion of the foe.