Attalus Antigonos had the immeasurable blessing to grow up on the great world of Macragge, surrounded by mythical and physical giants. The tales of Ventris, of Tigurius, of Sicarius and Calgar enshrined his early memories in rosy-hued splendor. His playfellows, like many of his father's line, were bred of houses known for producing battle-brothers through the centuries and millennia. He attended parades and drills and every speech he could to take sight of the glorious Adeptus Astartes throughout his youth, his determined gaze ever fixed on the adamantine sword they represented, mankind's greatest weapon in the fight for survival.

Yet Attalus was no giant. His mother was a PDF colonel of uncommon skill but of lower birth and stature than his father. Attalus was ever the smallest of his academy and was forced to rely on wit and will to carry what arm and leg could not. He passed the exposure trial by narrow margins, his geological studies allowing him to avoid a cross-country run by pinpointing a hidden mountain pass. His body accepted the Astartes implants with some reluctance, but he remained small by the standards of the mighty warriors he had grown to esteem so highly and who now surrounded him. Shorter of stride and strength, he felt ever behind his fellow initiates. He inherited the name Phoenos from a fallen battle-brother, one who was known for his valor, his resilience, and his faith, but the new Phoenos found it hard to accept his new name without the strength to live up to the accompanying virtues.

It was with the coming of the greatest titan of all that he would finally begin to find his way. The resurrection of the primarch was a planetary and system-wide evangelization, the most momentous and faith-renewing event in ten millennia, and Phoenos was at its heart. As the Great Rift spread and horror filled the stars, a new light shone from Holy Terra with ultramarine hue. Recruitment and training were redoubled across every sector, and Phoenos, along with nearly all his brothers, volunteered his name for Guilliman's Indomitus Crusade.

As dozens of vessels broached the Imperium Nihilus following the pilot light of the Emperor's burning blade, Phoenos met with both his greatest disappointment and his greatest hope. Guilliman's new sons, giants among giants, proud and fearsome and impregnable and devout, strode the halls of the dreadnoughts and battle barges like marble-cast saints. Phoenos had never felt so in awe, nor so crestfallen, as when he beheld their glory in battle, watching three primaris marines eviscerate a hundred greenskins in minutes. No matter how hard he trained, no matter what augmetics he acquired, no matter how devoutly he gave his live, he would never be able to achieve what these new heroes, these adamantine angels, could do for his chapter, for the Imperium, for the Emperor. He fell into brooding and despondency, sullen in his chambers and aloof in the field. His despair would prove short-lived.

The scout marines of the thirteenth chapter and its successors were given a great privilege—to behold an hour at the primarch's war arcade. Phoenos watched with rapt attention as the author of the Codex Astartes held council, heard briefs, listened to advisors, dispatched messengers and squads and companies and fleets, and managed the greatest Imperial war effort in the galaxy. The droning and minutia and paperwork and enforced decorum were a spectacle to the young neophyte, a revelation within him that answered the question of "how," how he could serve, how he could be uniquely useful to the Emperor, to his race, and to the Lord-Commander of the Imperium who sat above him. The battle-brothers of his company were larger, stronger, faster, and tougher. Primaris marines held every one of these and more with vantage. For every implant he had received, theirs was greater, for all the training he would complete, theirs was more. There was only one way in which he could match, could exceed the Emperor's finest; one organ for which he lacked an outright disadvantage and could give his chapter what others could not: his brain.

Harkening back to his days at the academy, Phoenos devoted himself to his studies with renewed vigor. He consumed texts and scrolls and dataslates like oxygen; reviewed Imperials maps, cartographic techniques, planetary geologies, terraforming, and military ideology; and memorized tactical programming and strategic axioms with as much rigor as he gave to his prayers. He developed a passion for resource allocation and the challenges presented by operating optimally with limited information. He could never be physically more than what he had already been granted by his chapter and fate—but his mind was limited only by his resolve, his memory limited only by his will. These were his mantras, the refrain of years as the crusade passed from system to system, darkness to darkness, star to star.

Eventually, fate demanded his separation from his idol and his support system. Dispatched on a mission to the Ustis system, he and his squad met with sterner resistance than they could handle. One of the three frigates in the flotilla was lost, another boarded. Phoenos fought against the renegade hordes, slaughtered man after man, watched his brothers and childhood companions die on jagged cutlass and bayonet. Separated from the rest, he ejected a now-empty boarding boat from the punctured side of the Imperatus Astra and descended to the craggy surface of Ustis III. The regret he felt for the Imperial losses in the stars above was sharp yet distant, his mind already processing the new trials and opportunities presented by his predicament. He did not resent the abrupt change in the pattern of his existence, merely the cost to the Imperium that had generated it. He looked at his new isolation on the sparsely-populated planet as a chance to prove himself worthy of his ideals. Month upon month of solitude was filled with regimen, calculation, meditation, and prayer as Phoenos waited for his chance to escape Ustis. His hearts were eager and his mind was clear as he joined a pilgrim caravan headed for the newly-designated fortress world of Mort Gideon, deep in the heart of the Dark Imperium which beckoned just beyond the bridge-deck.