Severin was an Imperial Navy Captain who served in Admiral Venesca Catallia's Battlegroup Silver Dawn during the 13th Black Crusade. As the Crusade raged across Segmentum Obscurus, the Admiral was ordered to aid Cadia and Catallia risked the Battlegroup's destruction by emerging from the Warp near the Fortress World. Severin complained about this, but his concern was dismissed by the Admiral, who led the Battlegroup into the void battle surrounding Cadia. When Severin saw the sheer number of Chaos forces attacking the Fortress World, he claimed it was doomed and they should retreat in order to save themselves. Admiral Catallia was incensed by Severin's cowardly remarks and demanded the Captain's Fleet Commissar do his duty. The Commissar complied and promptly executed Severin.