inquisitor Thrax

Once the Ultramarines became aware of what had occurred to Titus, Chapter Master Calgar made repeated requests to the Inquisition for the Captain's return. These were to no avail, however, as Calgar would never receive any replies regarding Titus or Inquisitor Thrax. In truth, Titus was repeatedly subjected to the same tests, that the Inquisitor's Space Marine prisoners endured aboard Thrax's watch station. This continued for a century, during which time the Inquisitor would also continue his persecution of Space Marine Chapters he deemed to be threats. He would be one of the first to voice concerns about the Astral Claws' Chapter Master, Lugft Huron, years before they caused the outbreak of the Badab War. Thrax also attempted to take custody of Darnath Lysander, so his purity could be tested after the Imperial Fist returned from being lost in the Warp for centuries. However, this would not come to pass, as Thrax was later overruled by the Senatorum Imperialis' Inquisitorial Representative. The Inquisitor also notably declared six Chapters to be Excommunicate Traitoris, which led to further blood being shed between the Space Marine Chapters. Then a century after the Graia Invasion, Thrax declared that the Grey Slayers Chapter had become corrupted and he led the Grey Knights in an attack that purged them all.

Thrax's gaze would later fall upon the Ultramarines Captain Demetrian Titus, during the Graia Invasion. By then, Thrax had over four hundred years of service and he ignored Graia's plight at first, when it involved Orks and the unblemished Ultramarines Chapter. It was not until Inquisitor's agents learned that the Chaos Lord Nemeroth had invaded the Forge World, that Thrax decided to get involved. After his arrival, though, the Inquisitor was contacted by the Ultramarine Leandros, who served in Captain Titus' Command Squad. According to Leandros, as Titus led the Ultramarines' 2nd Company against the invaders, the Captain had been repeatedly exposed to the Warp power source of the Psychic Scourge weapon, developed by Inquisitor Drogan. However, despite this, Titus miraculously emerged completely unharmed by the power source each time. Drogan was also revealed to have been possessed by a Daemon that served the Chaos Lord Nemeroth the entire time, that Titus had interacted with him. This led the Captain to be confronted by Thrax, after Graia had just been saved due to Titus' actions. Once he is faced with the Inquisitor's accusations of heresy, the Captain decides to surrender himself to Thrax, rather than resist. In this way, Titus ensures that the 2nd Company and the 203rd Cadian Regiment that had aided them, are free from the Inquisition's wrath for being affiliated with a potential heretic. Thrax would then order that Graia be quarantined due to the nature of its invaders and then departed from the world with Titus

A student of the Imperium's history, Thrax believed that Space Marines were a significant threat to Humanity, alongside heresy and the Warp. Since he was an avowed member of the Ordo Malleus, the Inquisitor made it his goal to monitor the actions of Space Marine Chapters, especially those who purported to keep the Imperium's borders safe. Thrax, however, would mainly keep his scrutinizing gaze on those Chapters that were operating within the Segmentums Solar and Tempestus. Regardless of their location, though, the Inquisitor would use his power to take action against those he believed were threats. As a result of this, Thrax took a number of Space Marines he considered to be Heretics into his custody and subjected them to repeated psychic scourges and brutal mindtrawls within his remote Inquisitorial watch station. Even if his tests proved they were innocent of his charges, though, Thrax would refuse to believe the results. Instead, the Space Marines would be returned to their Stasis Cells aboard the station, where they would remain until the Inquisitor decided to prove their guilt again by subjecting them to his tests once more.

Gerome Thrax was an Ordo Malleus Inquisitor Ordinary, who once served as an Interrogator to the legendary Daemonhunter Phaust.