Originally a Sergeant in the Fourth Company of the Sons of Guilliman Chapter, Constantinus and his squad fought in freeing the population of the world of Nova Terra from Tyranid attack and after driving the aliens off the world, his unit was left behind to monitor for signs of Genestealer infestation. For three years Constantinus led his squad on endless patrols through the caves of Nova Terra, cleansing planet of remaining pockets of Tyranid infestation. When rumor arose of a Genestealer infestation among the city of Cirtus' ruling aristocracy, Constantinus hunted down the infected nobles and their families brutally.
However the people of Nova Terra were enraged by the summary execution of their leaders and rose up in revolt. Disgusted by this "ungrateful" behavior and his will exhausted, Constantinus burnt down entire sectors of Cirtus, turning on those in his own squad who tried to stop him. He appeared before the crowd and announced himself the new ruler of Cirtus declaring the Emperor and his minions had turned him into such a monster. Constantinus vowed to lead the people of Nova Terra to freedom. Eventually commanding a 3 million strong army which overthrew the planets Imperial Governor. The renegade sergeant renamed the world of Nova Terra Constantinium and under his rule bloodthirsty mobs were given free reign, anarchy prevailed in the streets, and any dissent was viciously silenced.
Now uninhibited, the crowds eventually turned to worshiping the Gods of Chaos, which attracted the attention of Chaos Space Marine warbands. Constantinus fought and defeated the best Champions of Chaos, claiming their warbands for himself. He then embarked on a rampage across neighboring systems, and within a decade his wars had engulfed the entire Sector. Eventually, Imperial forces, including the Iron Knights and another two Space Marine Chapters, twelve Imperial Guard foundings, an entire battlefleet and agents of both the Officio Assassinorum and the Ordos Hereticus, arrived and after a thirteen year war reclaimed the world for the Emperor. The war itself only ended with the death of Constantinus himself at the hands of the Officio Assassinorum.
- 1: Codex: Chaos Space Marines (4th Edition), pg. 19
- 2: Codex: Chaos Space Marines (6th Edition), pg. 24
- 3: Liberator (Short Story) by Jonathan Green