"Merrick, a Guardsman's life is to die. My job has always been to send them where they can die. I'm not afraid to spend men, but I never waste them!"
- — Lord General Castor to Sergeant Major Merrick after the destruction of Typhon Primaris
Lord General Castor was a general officer of the Astra Militarum who served the Inquisitor Adrastia during the Third Aurelian Crusade. He hailed from the Fortress World of Cadia and led several Cadian Shock Trooper regiments, including the famous "Castellan's Own" -- the Cadian 8th Regiment -- to restore order in Sub-sector Aurelia.
After the Greater Daemon Ulkair and the Black Legion were defeated by the Blood Ravens Chapter on the Chaos-controlled world that had once been the sub-sector capital planet of Aurelia. The Black Legion did not retreat after their defeat but instead rallied to either the Renegade Blood Ravens Chapter Master Azariah Kyras or the Chaos Lord Eliphas to bring destruction to several planets in Sub-sector Aurelia.
Due to the Chaos incursion, the conflict between Blood Ravens still loyal to the Imperium and the Emperor and those who fell to Chaos influence of Azariah Kyras and his Honor Guard excluding Diomedes, Aeldari raids and remnants of the Tyranids ravaging Typhon Primaris left the sub-sector in ruin, disorder and turmoil.
The Imperium then sent the Lord General and several Cadian regiments to restore order in the sub-sector. Even with Cadian regiments, the local Imperial Guard garrison regiments and Loyalist Blood Raven Space Marines the conflict consuming the sub-sector raged on. To make matters worse for the Loyalists, several regiments betrayed the Emperor and swelled the ranks of the forces of Chaos due to its influence upon them.
After 10 Terran years of constant conflict, the sub-sector was placed under a decree of Exterminatus after the Imperial high command determined that the sub-sector was likely lost to the Archenemy. Before the Exterminatus fleet arrived in the sub-sector to carry out its mission, an Inquisitor of the Ordo Hereticus named Adrastia was requested by Gabriel Angelos of the Blood Ravens Chapter to investigate their Chapter Master for heresy, In this way, if Azariah Kyras could be removed and with him the stain of Chaos plaguing the region, the people of the Aurelian Sub-sector could be spared their looming execution.
During Adrastia's investigation, she requested help from Lord General Castor. Castor agreed, with Sergeant Major Merrick, Commissar Lord Bern, and a force of Guardsmen and Storm Troopers accompanying him to the Inquisitor's investigation and save the sub-sector from destruction in what became known as the Third Aurelian Crusade.
- Dawn of War II - Retribution (PC Game)