" I charge thee, foul spirit, whatever thy corrupt nature, along with all thy twisted minions now processing this servant of the God-Emperor, by the mysteries of his holy ascension and enduring sacrifice in the sacred chains of the golden throne, that you tell me by some sign thy name, and the day and hour of thy departure. I compel thee, moreover, to obey me to the letter, I who am a humble servant of the God-Emperor. Depart, then, despised transgressor. Depart and burn forever in the outer darkness that awaits thee and thy benighted kin!"
- — Extract from the "Codex Exorcisms"
Arch Exorcists are zealous priests of the Ecclesiarchy who relish combating the daemonic as a holy work that follows the example of the God-Emperor Himself. Within the Adeptus Ministorum of the Calixis Sector, there are those priests who chafe at the political restrictions that only allow the Inquisitors of the Ordo Malleus to combat the unclean and unquiet Warp entities known as daemons. A large proportion of those clerics who are aware of the existence and nature of daemonkind yearn to take the fight to them, to dispel them and cast them out of the material realm and back to the myriad hells that spawned them.
The senior members of the Adeptus Ministorum are aware that there are unclean and unquiet spirits lurking within the Warp, seeking to devour the souls of the faithful. The senior clergy fear the influence of these beings, and rightly so, for they are the antithesis of all for which the God-Emperor's church stands. The Calixian Ministorum is not tasked with combating these entities: that is the role of the elite Daemonhunters of the Ordo Malleus. However, some within the Calixian Ministorum refuse to stand by and allow such evil to go unchallenged despite the political restrictions placed upon them. A few senior clergy of the Calixis Sector, with the permission of Sector Synod Arch-Cardinal Ignator, maintain a small and secretive order of specialist clerics devoted to the expelling of Warp fiends from the material realm. The Arch-Cardinal risks offending the powerful and secretive Inquisition for enacting such dangerous measures. He reasons, however, that in these dark days, command of a cadre of skilled and devout holy warriors sworn to destroy daemons is a treasure beyond measurable price.
During the events on the world of Redemption when a daemonic assault erupted, this gamble paid off. Inquisitor Octus Enoch desperately fought to avoid invoking an Exterminatus on Redemption in the face of a daemonic incursion. Unable to procure Ordo Malleus resources due to the onset of a Warp Storm at the same time as the incursion, he petitioned the Ecclesiarchy to raise Frateris Militia regiments to combat the threat. Instead the local diocese sent three Arch Exorcists, who proved instrumental in defeating the daemonic assault. To this day, Inquisitor Enoch works closely with the Ecclesiarchy when pursuing daemonic threats and makes sure that Arch Exorcists are available to other members of the Ordo Malleus. When the Daemonhunters assist the Inquisitors of the Ordo Hereticus, Arch-Cardinal Ignator of the Calixis Sector and other Cardinals with Arch Exorcists among their staff often lend their services to Malleus Inquisitors seeking to strike down the enemies of the Imperium from within.
The Arch Exorcists use faith itself as a weapon against a daemon. Their prayers and hymns madden and deafen the servants of the Archenemy, and their holy symbols and gestures bind them. They castigate and berate the possessed, driving the daemon forth before them and freeing the victim -- often with fatal consequences for both. Such is the fiery faith of these individuals that they are permitted to study the foul texts of the Archenemy in order to learn the wiles of the daemon. However, unlike the Radical Inquisitors of the Ordo Malleus, they scorn using the methods of the Archenemy against him. They know better than anyone that using such methods are inherently corrupting, eventually turning the user into that which he hates most.
Becoming an Arch Exorcist
Adeptus Ministorum Clerics who have shown a particular aptitude for defeating daemonic opponents will be gently nudged by their superiors in the direction of the Arch-Cardinal's secret order of Arch Exorcists. Based in an obscure side chantry of the Cathedral of Illumination on Scintilla, the order poses as a harmless order of choristers, devoted to study and song. Here they peruse arcane and forbidden texts and memorise hundreds of holy exhortations crafted to smite the daemon.
- Codex: Grey Knights (5th Edition), p. 48
- Dark Heresy: Blood of Martyrs (RPG), pp. 66-67