Fulgrim
Fulgrim (also known as the Phoenician) was one of the twenty Primarchs created by the Emperor in the earliest days of the Imperium, just after the end of the Age of Strife. Fulgrim, like the other Primarchs, was sucked from Terra by the Gods of Chaos and placed on a far-away world in an attempt to prevent the coming of the Age of the Imperium.
History
Youth
The Primarch-child was found on the resource-poor world of Chemos. Dependent on interstellar trade for food, and cut off from the rest of the galaxy by ferocious warp storms, strict rationing and improvisation could not prevent the slow death of the people of Chemos. When the capsule containing the infant Fulgrim plummeted to the planet, the scouts who recovered the child pleaded with the leaders of the settlement of Callax to spare the child's life, as orphans were seen as a strain on already stretched resources and normally put to death.
Named after a long-abandoned god of the people of Chemos, Fulgrim soon became a legend in his own right. At half the age of his fellow workers, he was able to fulfil his obligations to the continual running of Callax with ease. He quickly grew to understand the technology he had to work with, and began to modify it, increasing efficiency dramatically. By the time he was fifteen years of age, Fulgrim had risen from the rank of worker, to become one of the Executives ruling the settlement. Learning of the gradual deterioration of both Callax and all the other settlements of Chemos, Fulgrim decided that he would save his world.
Under Fulgrim's leadership, teams of engineers travelled far from their factory-fortress, reclaiming and repairing many of the far-flung mining outposts. As minerals poured back into Callax, Fulgrim supervised the construction of more sophisticated and energy efficient machinery. As recycling efficiency grew to the point where Chemos was producing a surplus for the first time in years, Fulgrim began to foster a re-emergence of art and culture, aspects of humanity sacrificed in the struggle for survival. The other settlements allied themselves with Callax, and fifty years after arriving on Chemos, Fulgrim was its sole leader.1
The Great Crusade
It was not long after this that the planet's isolation came to an end. From the grey sky came a flight of dropships, armoured and battle-scarred, each bearing the same symbol, a two-headed eagle. On hearing of this, some fragment of memory stirred in Fulgrim. Chemos had no formal army, but the dropships' landing zone had been surrounded by the Caretakers, the police-soldiers responsible for maintaining order in the factory-fortresses. Fulgrim sent word to the Caretakers to stand down and allow the visitors from above into Callax.
In his spartan quarters, Fulgrim was faced by armoured warriors from the stars. Their faces bore the scars of many battles, and from their shoulders hung scrolls listing their achievements. Their armour and weapons were finely-worked, and their banners and pennants were works of art. Fulgrim recognised that these men were not merely advanced, but civilised - his lost brothers from the stars had preserved the arts he had longed to return to Chemos. From the midst of these warriors stepped their leader, the Emperor of Humanity. Fulgrim surveyed him and, without a word, knelt and offered his sword. On that day Fulgrim swore to serve the Imperium with all his heart. From the Emperor, Fulgrim learned of the distant world of Terra, of the Great Crusade to reclaim the sundered galaxy, and of his own origins. It is unknown when exactly this event occurred; however, it is recorded that the construction of a starship for the Primarch of the III Legion was completed around 160 years before the beginning of the Horus Heresy.2
Travelling to Terra to meet his new Legion, Fulgrim learned that an accident had destroyed the majority of the gene-seed designated for his legion, and without their Primarch, replacing it was a slow and laborious process. Fulgrim came to address the two hundred Space Marines of his legion, and the words he spoke were said to inspire the Emperor so much that he named the legion the Emperor's Children, and allowed them to bear the sign of the Aquila, the double-headed eagle that was the Emperor's personal symbol, on their power armour.1
Fulgrim became driven by the notion that his Legion should strive to live up to this honour and the perfection of the Emperor and his vision of Imperial culture. This drive to achieve perfection soon applied to all things the Primarch and his Legion became concerned with, from military tactics to the embrace of artistic culture that didn't exist on Chemos to their very appearances. Fulgrim was a particularly imposing sight, with shimmering white shoulder-length hair, large, friendly-seeming eyes and a mouth that was never far from a smile. His armour was of the finest quality, and intricately decorated. Over it he often wore one of a variety of high-collared cloaks.2
Fulgrim was anxious to make his contribution to the Great Crusade, but the comparatively small size of his Legion meant that the Emperor's Children were placed under the command of Horus and his Luna Wolves. Horus and Fulgrim grew close to one another while pacifying the Eastern Fringe. Eventually, swelled by recruits from both Chemos and Terra, Fulgrim was soon able to lead a crusade of his own, bringing countless worlds into the light of the Imperium.1
During this time, the Emperor's Children initiated the Cleansing of Laeran, a campaign that required great effort, dedication and sacrifice from the Imperial forces. At the conclusion of this campaign, Fulgrim acquired a trophy from the field of battle; a xenos-manufactured sword recovered from a Laeran temple. He would begin to wield this sword more often than Fireblade, his customary personal weapon. With the benefit of hindsight, it can be recognised that the Laeran sword was a Daemon Weapon.2
Horus Heresy
It is now believed that this daemonsword began to exert a strong chaotic influence over Fulgrim, and that the forces he had deployed against the Laer may have become tainted by the Chaos power Slaanesh. It is in this parlous spiritual condition that Fulgrim found himself at the centre of the emerging Horus Heresy.1
Fulgrim himself met with the renown Farseer Eldrad Ulthran of Ulthwe on the Maiden World Tarsus, in which the Farseer attempted to warn Fulgrim of Horus' grievous wounding at the hands of Eugen Temba and his Anathame, and how he was slowly beginning to turn to Chaos as he recuperated. Fulgrim reacted with outrage at the Farseer's accusations due to his close friendship with Horus, second only to his bond with Ferrus Manus. This was spurred on by the influence of Fulgrim's Laeran blade, which was infused with a Slaaneshi entity. Fulgrim furiously attacked Eldrad alongside his captains and the Phoenix Guard, destroying both Khiraen Goldhelm, an ancient and revered Wraithlord as well as an Avatar of Khaine in the process, forcing Eldrad and his beleagured forces to withdraw. This victory to Fulgrim's subsequent destruction of various Eldar maiden worlds using virus bombs as a means to end the supposed treachery of the Eldar. 2
Whilst the exact timing and placement of it varies between versions of the story, it is clear that Fulgrim soon met Horus in person, demanding a personal account of his actions. Instead, Horus was able to sway Fulgrim to his cause. Fulgrim's respect for Horus allowed Chaos to find it's way into Fulgrim's heart, destroying Fulgrim's loyalty to Terra, and replacing it with burning desire to destroy the man who held humanity back from the perfection Fulgrim desired.1
Fulgrim was immediately sent to meet with Ferrus Manus, Primarch of the Iron Hands. Great bonds of friendship and brotherhood existed between them, and Fulgrim felt that he could convince Ferrus of the righteousness of Horus' cause. He was wrong however, and their meeting did not go well, and concluded in violence. When next the brothers met, it would be as enemies.
Their path chosen, the chaotic rot spread quickly, from Fulgrim to his lieutenants, the Lord Commanders of the Legion, then to company and squad leaders, and finally all but a bare handful of Marines followed Slaanesh rather than the Emperor. Perfection became perfect hedonism. When the loyalist legions arrived in the Isstvan system, the Emperor's Children were at the forefront of the fighting, aiding in the massacre of their former brethren. During the infamous Drop Site Massacre, Fulgim and Ferrus Manus met once again, and had their final and fateful duel. Fulgrim proved the victor, but discovered he could not bring himself to kill his brother. It was at this point that the daemon bound within the Laeran blade fully exerted itself, and Ferrus Manus was struck dead. Fulgrim was shocked into clear-thinking by the death of his brother, aghast at what he had done and at the horrific betrayal and carnage around him. In a further moment of weakness he agreed to the daemon's offer to send him to oblivion and allowed the warp-creature to escape from the sword. It took but a moment for it to posses him body and soul, trapping his consciousness in tiny corner of his mind. From that moment on, Fulgrim became a prisoner in his own form, his existence fully controlled by the Slaaneshi daemon.2
Horus' rebellion spread, bringing the entire Imperium into civil war. All trace of decency amongst the Emperor's Children had vanished by the time they partook in the Siege of Terra. While other Traitor Legions assaulted the Imperial Palace, the Emperor's Children embarked upon a spree of terror and gratification amongst the helpless citizenry of Earth. Billions of defenceless civilians were used as experimental subjects in the effort to create ever-more powerful stimulants and pleasure-inducing chemicals, used to suffer daemons, or were simply killed to sate the bloodlust of the Legion.1
After the Heresy
When Horus was defeated by the Emperor, the Emperor's Children left a trail of depopulated worlds in their wake as they fled towards the Eye of Terror. As their supply of slaves was exhausted, they resorted to raiding the other Traitor Legions for fresh meat, and in the end were crushed by their angry brethren in a series of bloody wars. Finally, the Emperor's Children were shattered into bands of hedonistic fanatics. Warbands of the Emperor's Children are thankfully rare, for there is no fate worse than falling prisoner to them.
As to the daemon who had taken over Fulgrim, it was elevated by Slaanesh to the rank of Daemon Prince - gifted with a serpentine form and multiple arms holding rapiers - and now rules over a planet of unending, unlimited pleasure. To this day, warbands of Emperor's Children and the Imperial Inquisition seek this world, but none have returned. Fulgrim himself was last seen in combat with Roboute Guilliman, the Primarch of the Ultramarines, where he slashed his brother's throat and laid him low with a fatal poison.