Brother Severus arrived on Macragge as one of sixteen aspirants who had triumphed in competitive games between Quintarn, Tarentus, and Masali. These games are held between the triple worlds each seven years to determine which youths should have the honour of attempting to join the Ultramarines Chapter on Macragge. The games which Severus participated in were noted as particularly spirited and hard-fought on this occasion, with over a third of the participants killed or seriously injured. The young Severus was accepted by the Ultramarines and successfully completed his training. According to records, Brother Severus’ early career in the Scout Company was unremarkable, but once he came to full status as a battle-brother he was frequently commended for his wisdom and far-farsightedness. He received his Marksman’s Honour while a member of the 6th Company in in combat against Eldar pirates, and an Imperial Laurel in the following year after being wounded in the cleansing of Copul IV. He was was promoted to Sergeant in the 3rd Company and commanded his squad through the Siege of Belios and the first Balur Crusade, earning great praise from his company’s Captain.
When Sergeant Severus led his squad in breaking through a dangerous Ork encirclement on Goramon he was inducted into the prestigious 1st Company. His promising career was cut tragically short, however, when he was critically injured during the Battle of Corinth. Ultramarines Apothecaries used his mortal remains to replace those of Venerable Brother Commodius, whose Dreadnought frame was also damaged on Corinth. Severus adapted well to the transition into the amniotic tomb of a Dreadnought body, retaining all of his former wisdom and battlecraft. Severus’ list of battle honours over the succeeding three centuries grew too long to be listed, culminating in his eventual return to Corinth during the seven year Corinthian Crusade. Brother Severus also participated in the Damocles Crusade against the Tau Empire, but urgent new orders sent his company back to Macragge to defend it from the advance of Hive Fleet Behemoth. During the ensuing Battle of Macragge, he fought with the 3rd Company and slew a Hive Tyrant in close combat. This was the first accredited kill of such a creature in Imperial history.