Cyrius was a Lord Commander of the Emperor's Children Traitor Legion during the Great Crusade and Horus Heresy eras. He was known to have been the second opponent to defeat Lucius the Eternal in combat, only to have his victory cut short when his body was slowly and painfully transformed into a newborn copy of Lucius as the result of a gift provided to the Soulthief by Slaanesh, the Prince of Chaos. Slaanesh did not wish to see one of his favoured Champions and proteges removed so easily from the Materium. Cyrius slowly and painfully transformed into Lucius over a matter of weeks. The former Lord Commander now exists only as a screaming and writhing face upon Lucius' Armour of Shrieking Souls.
Following the corruption of the Emperor's Children by the Ruinous Powers the arrogant Captain Lucius continued to distinguish himself in the arts of war as his Legion traced the downward spiral of Chaos worship. The gaudily-painted fleets of Fulgrim's Traitor Legion moved from world to world, bringing ever more vile and extreme deaths to the populations that became their prey. In the transitory times between each invasion, the Emperor's Children would indulge in pageants of violence and gladiatorial contests amongst themselves. Only the most inventive displays of bloodletting could stay their boredom for long.
Whenever he fought in these contests, Lucius truly excelled. His obsession with becoming the perfect swordsman lent him speed and skill that even other Space Marines could not match. The joy he took in both giving and receiving the hot kiss of agony was so intense that it echoed in both in the material dimension and the Warp. Some even whispered that Lucius had been brought back from the brink of oblivion more than once, and that his obsession was stronger than death. Lucius' infamy grew in this realm and the next. Before long, it was not only the Emperor's Children that drank in each of Lucius' orgies of bloodletting, but the handmaidens of Slaanesh that clustered around his reflection in the Empyrean. After each contest, he basked in the adulation of his fellow Traitor Legionnaires, bowing elaborately and fanning the applause with his blade. His grandstanding was such that it eventually drove the silver-maned Lord Commander Cyrius to action.
As the contest known as the Scarlet Blade reached its final round, Cyrius himself stepped into the arena against Lucius. The Lord Commander intended to teach the preening champion his place and cement his own position as Fulgrim's favoured son in the process. Clad in baroque artificer armour painted with obscene dreamscapes and wielding a twelve-foot power spear, Cyrius made for an impressive opponent indeed.
The Lord Commander was every bit as fast as his chosen foe. Lucius fought hard to get within the reach of the power spear, ducking and rolling with fluid grace. Weapons clashed and clanged in a staccato blur. Though Lucius' blade was sharp as a razor, it could not penetrate Cyrius's ornate battle plate, and for his part the swordsman was wearing little more than a sleeved tunic. A well-placed kick from Cyrius sent Lucius sprawling backwards, coughing blood. A stab of the power spear took a finger from Lucius' sword hand. Less than a second later, a sidelong blow from the power spear’s haft sent starbursts across the swordsman's vision.
Each fresh wound had sent Lucius giggling with glee. Cyrius bared his teeth, slashing and jabbing as his opponent laughed, staggered and whirled across the scarlet sands like a demented marionette. At the last, Lucius corkscrewed through the air and levelled a decapitating blow right at Cyrius' throat. There was a sudden crack of electrical discharge from the impact, and Lucius' blade snapped in two. As the crowd howled and hollered around him, Lord Commander Cyrius caught his laughing opponent by the throat. Grinning a mirthless smile, he pounded Lucius into the scarlet sands of the arena until there was nothing left but a red ruin of broken bone. The Emperor’s Children had lost their favoured duellist, but gained a memory to be savoured for years to come.
Over the next few weeks, Lord Commander Cyrius underwent a hideous transformation. His mane of hair fell out in clumps, his eyes changed colour, and the copulating figures that decorated his armour writhed and flowed to depict a host of laughing Daemons. To the commander's mounting horror, dark lines appeared under his flesh, pushing outward with each passing night until they formed a maze of scar tissue. His screams were a source of great interest to his fellow Emperor's Children, but none came to his aid. In the Lord Commander's fate they saw the hand of Slaanesh at work. Some swore that Cyrius' shrieks changed in tone, becoming ever more like maniacal laughter. The next gladiatorial event saw Lucius stride the sands once more, his power armour adorned with the tortured, moaning face of Cyrius. The heavily scarred swordsman had been reborn, and the Lord Commander had been taken in his place. In the throne at the arena’s edge, Fulgrim smiled knowingly. His master Slaanesh was evidently loath to let such an entertaining protege fall from the mortal coil for long.
Since that day, Lucius has borne a peculiar blessing from his patron, Slaanesh. Whoever takes his chosen champion's life, and finds even a moment of satisfaction from the act, will find himself undergoing a painful and gradual metamorphosis. When the transformation is almost complete, Lucius emerges from their discarded shell like a butterfly from a chrysalis. All that remains of his killer will be a screaming face trapped forever in the fleshy panels of his twisted battle plate.
- Codex: Chaos Space Marines (6th Edition), pg. 62
- Codex: Chaos Space Marines (4th Edition), pg. 54
- Codex: Chaos Space Marines (3rd Edition, 2nd Codex), pg. 57
- Warlords of the Dark Millennium: Lucius the Eternal, pp. 10-11