Simeon is a Blood Angel who served as the second-in-command of Captain Tycho's Company when they were tasked with quarantining the Hive World Orilan. Though they were ordered to destroy any ships that escaped from Orilan, which had become corrupted by Daemons of Tzeentch, Simeon convinced Tycho to lead a squadron aboard one such ship, when the Inquisitor Ramius Stele contacted their Frigate and requested their aid; after a Daemon from the planet, had boarded his ship and began mutating it. Disaster struck however, when Tycho returned with the Inquisitor and a small number of passengers from the corrupted ship, as the Codicier Varon shouted that one of them had been infected by the Daemon. The warning came too late though, as the Daemon erupted from the passenger and killed Varon before beginning a massacre aboard the Frigate.
Despite their efforts to defeat the Daemon, it later entered the Frigate's engine room and Simeon was ordered to remain outside, as Tycho led Inquisitor Stele and squadrons of Blood Angels into the Daemon's lair before sealing the entrance. Simeon later disobeyed his orders, after they had not returned, and found the site of a slaughter house, as his Brothers lay in pieces all over the engine room. All was not lost however, as Simeon later found the Inquisitor and the unconscious Tycho. With no sign of the Daemon, Simeon realized the exhausted Inquisitor had used his powers to banish it and later joined the other surviving Blood Angels in praising Stele. After Tycho was tended to, the Blood Angels decided to bring Stele to their Fortress-Monastery on Baal, where a blood debt, which is a rare gesture of respect and trust amongst their Chapter, would be granted to the Inquisitor. It was unknown to the Blood Angels present at the time, that this act would later set in motion a series of events, that would have dire consequences for their Chapter.