Thadus Valconet Horst

Horst in Battlefleet Gothic: Armada

Thadus Valconet Horst is a member of the Holy Inquisition, and was its most ranking member during the course of the Gothic War. He advised the command of the Imperial Navy during the course of the conflict. His primary interest was tracking down and retrieving to particular Chaos Artifacts -- the Hand of Darkness and the Eye of Night, both of which were stolen from the worlds they were held before the start of the Black Crusade.

While nothing is stated outright, it can be presumed that he is a member of the Ordo Malleus.

After the Gothic War

Inquisitor Horst continued his pursuit of the Eye of Night, and his investigations eventually led him to Moriana. The Chaos seer offered the artifact, in exchange for slaying a daemon that didn't keep its deal with her. Horst accepted, but he and his retinue of Grey Knights were no match for the Daemon, and in the end his body was possessed by it. In desperation, Horst piggy-backed his soul onto the body of a slain Grey Knight paladin, then teleported it to the ruined world of Savaven.

Centuries later, Inquisitor Katarinya Greyfax was tasked by Roboute Guilliman to retrieve the Eye of Night. The clues that were left behind led her to the ruins of Savaven, where she found the undead Horst, now suffering a bit of amnesia. Despite this, Horst agreed to aid Greyfax, and together the two went to the Eye of Terror to consult Moriana (again). The two inquisitors then tracked down Horst's possessed body, and in the battle that ensued, slayed the demon, though Horst was given a final death in the process.

In the end, it turns out that the Eye of Night was inside the Grey Knight power armor that Horst was inhabiting. Greyfax returned the artifact to Guilliman, who in turn gave it back to the Inquisition for safekeeping.