An Inquisitor is a clandestine agent and highest-ranking member of the Imperial Inquisition. They are the secret policemen and intelligence agency of the Imperium, driven by ancient order of the Emperor of Mankind to ensure the security of the Imperium of Man from the taints of Chaos, the daemonic threats of the Warp and the dangers presented to Mankind by intelligent alien species like the Orks, the Tyranids, the Eldar, the Necrons and the Tau. Split into three main Orders, the Ordo Xenos (Alien Hunters), the Ordo Malleus (Daemon Hunters) and the Ordo Hereticus (Witch Hunters), the Inquisition is ruthless in uncovering and snuffing out Chaotic corruption, heresy, and mutation wherever they may be found among the million worlds of Mankind. The relentless and deadly agents of the Inquisition have infiltrated every facet of human society to insure that Chaos can never again take root in the Imperium, and that no alien race will replace humanity as the dominant intelligent species of the Milky Way Galaxy.
Throughout their career, Inquisitors will form their own cadre of agents of various roles and functions in order to achieve whatever goal is put before them. These agents fall into two classes, known as Acolytes and Throne Agents. Acolytes are initiates into the Inquisition's service who may eventually become Inquisitors themselves one day if they perform well and please their master; Throne Agents are mature Acolytes who have served the Inquisition and a particular Inquisitor for years and sometimes decades. They are among the most powerful beings in the Imperium of Man after an Inquisitor himself. Some of these agents are common tools used throughout the Imperium, including priests of the Ecclesiarchy, Astropaths, Servitors, Tech-priests of the Adeptus Mechanicus, etc. Others may be more subtle and even serve a more specific role, such as high-ranking members of the Administratum, the apprentice Inquisitors called Interrogators, elite members of the Imperial Guard like Storm Troopers or the Adeptus Arbites' Judges, and the highly-trained Assassins of the Officio Assassinorum's four temples or various Imperial death cults. Any member of any organisation within the Imperium that can help in achieving an Inquisitor's objective will likely serve a purpose for the Inquisition at one point or another. Some may be used briefly for special tasks or one-shot missions while others may serve alongside the Inquisitor for the duration of their career. Over time, older, more experienced Inquisitors will have built an extensive network of spies and agents that make seeking out and destroying threats to the Imperium all the easier.
Potential Inquisitors are often drawn from the Progena (graduates) of the Schola Progenium who show the most promise in intellectual or psychic areas prized by the investigative arms of the Inquisition. As is the case with all aspects of the Inquisition, the matter of recruitment is not a centralised process but the power to recruit is left in the hands of the individual Inquisitors. Some Inquisitors are known to not recruit at all and instead spend their years of service in pursuit of their enemies as well as dedicating their hours to duty for the rest of their lives. Others, however, feel that it is one of their many burdens to bring about the next generation of Inquisitors who are destined to carry forth the battle that the Inquisition must wage on behalf of humanity. Ultimately, the matter is left to the judgement of the individual Inquisitors who are subject only to the scrutiny of their peers, as is the case in most matters. A majority of Inquisitors typically leave such matters to chance or perhaps to Fate in regards to picking a suitable candidate from amongst the groups of individuals whose paths cross that of the Inquisition. There are a number of Inquisitors who are more rigorous in regard to the pursuit of Acolytes and will spend a proportion of their time seeking suitable candidates -- often from the ranks of other Imperial Adepta.
There exists no set criteria in regards to physical condition for a possible candidate when being selected to join the ranks of the Inquisition. All that is required is proof of intelligence and loyalty to the Emperor of Mankind which are key requisites for such a choice. There is no proper method of judging these attributes until later in life. However, there may exist an extraordinary circumstance which leads to an Inquisitor choosing a boy or girl whilst they are still within their teens if the subject shows exceptional ability. Generally, an Inquisitor will take note of an individual if they are a free-thinking person with great willpower and determination as well as unflinching principles. If a suitable candidate is found, they will become part of the Inquisitor's retinue as an Acolyte where they may serve in a minor capacity whilst the Inquisitor continues their evaluation. Those that later prove their worth whilst working with the Inquisitor can be taken into the greater confidence of their master.
Over the years of his or her service, the Acolyte will begin to learn what they can of the Inquisitor's knowledge and their many duties. Certain Inquisitors often refer to these apprentices as Interrogators, though they are also known as Novitiates, Neophytes and as Approbators. At this stage, the individuals can undertake missions of their own or control operations in concert with their master or mistress, though ultimately they are still subordinate to them until the Inquisitor agrees with several of his peers that one of his Acolytes is ready for the responsibilities that come with being a full Inquisitor. In normal conditions, the consent of three Inquisitors or a single Inquisitor Lord is needed to bestow the full powers of an Inquisitor on an Acolyte as well as grant him or her the Rosette of the Inquisition. There have been rare occasions which warrant an Acolyte taking on full Inquisitorial powers immediately. This is likely the case when the Inquisitor in charge has been killed during an ongoing operation, which requires the Acolyte to immediately inherit their master or mistresses' position.
Acolytes may pass from one Inquisitor to another as fate dictates and through this way, the ideals of the Inquisition are passed on. This in turn allows the various competing factions and institutions of the Inquisition to propagate across the centuries. In addition to his master or mistress' personal philosophy on the duties of the Inquisition, the Acolyte also learns what their teacher knows of the internal, byzantine political workings of the Inquisition. However, such knowledge cannot be freely given and it cannot be taken without effort as that would devalue the knowledge itself. This goes in line with the Inquisitorial saying "Knowledge is power; guard it well."
All Inquisitors begin as Acolytes, apprentice-Inquisitors given over to the tutelage of a full member of the Inquisition. Acolytes accompany a fully experienced Inquisitor in his Inquisitorial duties. He may perform a number of tasks for his superior, including serving as warrior, scribe, and interrogator. After a set amount of time, his master will provide a recommendation on his behalf to one of the Ordos of the Inquisition to advance his pupil to full Inquisitorial rank. After this recommendation is accepted by three full Inquisitors or an Inquisitor Lord as noted above, the Acolyte is raised to the rank of a full Inquisitor and can initiate his own agenda and operations. Although the new Inquisitor is no longer bound to his old master, they will have formed a personal bond and may work together and help one another in the future.
As the most important arm of the Imperial government dedicated to ensuring the security of the Imperium of Man, the authority of the Inquisition technically supersedes all others, including, in theory, a High Lord of Terra or even a Chapter Master of the Adeptus Astartes. Thus, Inquisitors have access to an almost limitless variety of Imperial resources that allow them to act in full strength against any threats they perceive to the Emperor's domain. Despite this comprehensive legal authority, experienced Inquisitors seeking the assistance of the Space Marines or the knowledge and resources of an Arch Magos of the Adeptus Mechanicus have learned to act with discretion towards such powerful Adepta of the Imperium. Uniquely, Inquisitors have been known to use a wide variety of artefacts and wargear throughout their careers as a result of such heavy interaction with the other Adepta of the Imperium and even xenos cultures. Despite their seemingly powerful capabilities, even the Inquisition may not be able to fight back a rampant and well-rooted infection of Chaos or unusually powerful xenos forces like a Tyranid Hive Fleet. On worlds where such infections have been discovered, an Inquisitor may condemn the planet to Exterminatus, the ultimate Imperial sanction which is granted only to an Inquisitor or a Space Marine officer to unleash upon a world.
To truly understand Chaos is to be consumed by it, and such dealings with the horrors of the Warp often requires an near-heretical interaction with the Forces of Chaos by a given Inquisitor, especially among the members of the Ordo Malleus and the Ordo Hereticus. To effectively battle and exterminate Chaos, some Inquisitors, especially those of the Radical persuasion, believe that they must fully understand and tinker with its workings in order to fight it more effectively. However, such actions are either deemed heresy by Puritan Inquisitors or cause the Inquisitors themselves to fall victim to the corruption of Chaos. Such individuals are named Excommunicate Traitoris by their fellow Inquisitors and as such will be hunted down and destroyed at the first opportunity like all such enemies of the Emperor.
- Agmar - As a young member of the Ordo Hereticus, he lead attacks upon Ichar IV's capital city of Lomas to break up rebellion among strange cult members. It turned out that the rebellion was created by a massive Genestealer infestation. With the Adeptus Arbites, he destroyed enough defenses to allow the Ultramarines to seize the planet. It was then that Angmar's Astropaths felt the approach of Hive Fleet Kraken and it was his initiative that led to the breaking of Hive Fleet Kraken at Ichar IV.
- Ario Barzano - Member of the Ordo Xenos. Barzano disguised himself as an Adept of the Administratum on the planet Pavonis in order to help the Ultramarines stop the awakening of the C'tan called the Nightbringer. He dies in the attempt and is buried on Pavonis.
- Covenant - One of a new breed of Daemonhunters who hunts down traitorous members of the Inquisition itself and their Daemonhosts. He trained the Inquisitor Ivixia Dannica. Covenant is equipped with a Power Falchion, a Psycannon and limited psychic powers.
- Torquemada Coteaz - An Inquisitor Lord of the Ordo Malleus and High Protector of the Formosa Sector, a title he took from Inquisitor Laredian when it was revealed that Laredian created Daemonhosts and other abominations. Coteaz is an infamous adversary and destroyer of daemons; his name is a reference to the medieval Spanish Inquisition leader Tomás de Torquemada.
- Bronislaw Czevak - One of the few non-Eldar to gain access to the infamous Black Library. Czevak reported the destruction caused against the Eldar Craftworld Iyanden and its supporting spacefleet by the Tyranids.
- Ivixia Dannica - After her father Colonel Dannica was murdered by a daemon summoned by cultists who wanted revenge for the purge he enacted on them and their brethren, Daemonhuntress Ivixia was trained by Covenant. She had her father's skull fitted with an autogun and fitted to her armour so he could serve the Emperor beyond death. She wields a Power Halberd made from the shards of Saint Josmane's armour. The weapon is filled with the power of the saint and has sent scores of daemons screaming back to the depths of the Warp.
- Jaq Draco - Jaq Draco is the main character in the Inquisition War series of novels. Draco gained access to the Eldar's Black Library and stole the Book of Rhana Dandra. Draco is also one of the few individuals in the galaxy to have entered the Emperor's Sanctum Imperialis and have an audience with the Emperor of Mankind since his internment in the Golden Throne. Draco has, for much of the Inquisition War Series, a retinue consisting of a Navigator, an Assassin and a Squat. He is a formidable psyker.
- Drogan - Inquisitor Drogan was a Radical Inquisitor of the Ordo Xenos] who developed an arcane technological device capable of opening up multiple portals into the Warp. Drogan was slain and his body possessed by a Daemon from the Warp at the direction of the Chaos Sorcerer Nemeroth, who used him as a pawn to trick the Ultramarines 2n Company, under the command of Captain Titus, who had arrived on the beleaguered world of Graia to bolster its defences, for the vital Forge World had been invaded by a large Ork WAAAGH! composed of over 1 million Orks led by the Warboss Grimskull. It was Drogan's intent to trick the Ultramarines into activating the archaic device. The rogue Inquisitor had deceptively named the device the Psychic Scourge, and claimed that it could kill all of the Orks invading the planet by overloading the Greenskins' gestalt psychic field of WAAAGH! energy and destroy their minds. Instead the Psychic Scourge was actually intended to open portals into the Warp from Realspace and bring the Chaos Sorcerer Nemeroth, a horde of daemons and the warband of Chaos Space Marines known as the Chosen of Nemeroth to the Forge World. The Sorcerer then appeared to extract some sort of "essence" – manifested as purple light – from Drogan, whose body fell to the ground, lifeless.
- Gregor Eisenhorn - An Amalathian member of the Ordo Xenos, he was the infamous Inquisitor who orchestrated the downfall of Quixos the Bright and Pontius Glaw using a stolen daemonhost named Cherubael, a former tool of Quixos. He seemingly vanished soon after the downfall of Pontius Glaw. Eisenhorn changed over the course of his career from being a staunch Puritan Amalathian into a Radical Inquisitor through the justified choices he made. These choices included keeping the Malus Codicium for himself, and trying to save his comrades from the attack of Cruor Vult (a Chaos Warhound-class Scout Titan) by summoning Cherubael. Gregor also caused the downfall of many other foes, including Beldame Sadia, Mandragore, the House of Glaw, Cruor Vult, and the rogue Inquisitors Lyko, Molitor and Quixos.
- Silas Hand - He is an important character of Daemonifuge, a graphic novel by Kev Walker. He was first a Witch Hunter serving under the Ordos Solar and eliminated thousands of heretics. After being approached by an important Daemonhunter, Inquisitor Lord Hephaestos Grudd, he was invited and joined the Ordo Malleus. Inquisitor Hand was sent to Ophelia VII to identify if Ephrael Stern was tainted by Chaos. Mysteriously, she was the sole survivor out of 12,000 Imperial Guardsmen that were sent to the planet Parnis. His investigation led to no conclusion, and Hand was forced to return with her to the planet Parnis. During the return, their vessel's Navigator was possessed by Chaos and destroyed their starship the Hammer of Thor. Escaping, both Hand and Stern were able to land upon the surface. However, they soon confronted the Daemon Q'tlahsi'issho'akshami. Only Stern managed to live through the battle.
- Jason Hunt - Ordo Malleus Inquisitor and Warden of the Stromgard Sector. Hunt is closely affiliated with Commander Marcus Flintlock of the Storm Dragons Space Marines, and has used detachments of that force frequently in pursuit of his missions. He is also a high-level psyker.
- Lady Helen Jerico - An Ordo Xenos Inquisitor. She has had numerous dealings on the planet Necromunda. Mother of bounty hunter Kal Jerico.
- Inquisitor Lord Fyodor Karamazov - An Inquisitor Lord of the Ordo Hereticus, also known as the Pyrophant Judge of Salem Proctor. This is a reference to Authur Miller's The Crucible, Proctor being the name of one convicted, yet innocent, witch; and Salem being the Puritan township he lived in. A staunch Amalathian, Karamazov habitually judges and does battle from his massive Throne of Judgement and is generally hated by the Ecclesiarchy and Thorian Inquisitors for his actions on Salem Proctor. His name is a reference to Fyodor Dostoevsky, Russian author of the novel The Brothers Karamazov, which contains a parable entitled The Grand Inquisitor. Karamazov made the infamous quote that is used to sum up an Inquisitorial investigation: "There is no such thing as a plea of innocence in my court. A plea of innocence is guilty of wasting my time."
- Kryptman - Member of the Ordo Xenos, Tyranid expert, saviour of the Imperium in the Hive Fleet Leviathan crisis, and the discoverer of a full 82 new alien species (all of which he subsequently deemed a threat to the Imperium and ordered eradicated). Kryptman was the first Inquisitor to witness the devastating effects of a Tyranid invasion during the attack of Hive Fleet Behemoth and fought the Tyranids for over 250 years. He was one of the most active members of the Inquisition against the Tyranid invasions, even taking drastic measures to the dismay of other Inquisitors. During the Invasion of Hive Fleet Leviathan, Kryptman led Deathwatch kill-teams to the Tarsis Sector to aid the Mortifactors Chapter and the Ultramarines of Tarsis Ultra. By capturing a Lictor, Magos Biologis Locard (Kryptman's Adeptus Mechanicus biologist) created a biological weapon to use against the Tyranids and his Deathwatch members used it to destroy the Norn Queen. Kryptman later authorised the largest single act of genocide the Imperium has ever inflicted on itself by abandoning or destroying all worlds in Hive Fleet Leviathan's path. He was later issued a "Carta Extremis" and was stripped of his title. However, this did not stop him and he soon led his loyal Deathwatch warriors to steal Genestealers in stasis and used them to lure Tyranids to the homeworlds of the Orks of Octavius .
- Ligea - Inqusitor Ligea can be described as "Looking more like an elegant family matriarch rather than a hunter of daemons." Ligea was an unusual Inquisitor, in that she did not see much combat, but rather focused her efforts on texts and ancient writing. She possessed at least one minor psyker ability, which allowed her to apprehend information simply by contacting an object, such as a book or a statue. She was recruited into the Ordo Hereticus at a very young age. One of her most notable parts was in the novel Grey Knights by Ben Counter, which tells the tale of Ligea, and how she was attached to the Grey Knights on the trail of Saint Evisser, looking for Ghargatuloth, Prince of a Thousand Faces, a powerful daemon of Tzeentch. Unfortunately, Inquisitor Ligea eventually succumbed to the taint of Ghargatuloth after allowing herself to delve too deeply into tainted knowledge, opening her mind to daemons which caused her to lose her mind. Having gone quite insane and fallen mostly to Chaos in the process, Ligea was captured by the Inquisition she once served. However, having opened herself up to Ghargatuloth, she was able to learn and reveal the true name of Ghargatuloth to Justicar Alaric, through a recording of her interrogations, in which she babbled what was apparently a meaningless string of syllables. This gave the Grey Knights the advantage they needed in order to destroy Ghargatuloth every thousand years. Inquisitor Ligea died in an interrogation room high above the planet Mimas when Inquisitor Nyxos ordered her cell opened to space.
- Solomon Lok - Member of the Ordo Xenos, lead the investigation of the loss in communication from Beta Anphelion IV, supported by Space Marines from the Red Scorpions Chapter, along with the Eylsian drop troop regiment D-99 and also a regiment from the Cadian Guard. Featured in Imperial Armour IV, and one of the few Inquisitor models cast by Forge World.
- Xavier Mendoza - Xavier Mendoza is possibly one of the most notorious Inquisitors in the history of the Imperium of Man. A fanatical man, he quashed Chaos wherever he found it. Active in the later centuries of the 31st Millennium following the Horus Heresy, he became convinced that all Space Marines were the secret servants of Chaos because of the betrayal of the Chaos Space Marines during the Heresy. He began an all-out holy war against the remaining Loyalist Adeptus Astartes. Mendoza's action came to a head when he boarded a Chapter cruiser of the newly-formed Black Templars, a Successor Chapter created from the Imperial Fists Legion during the Second Founding. He accused the crew of harbouring daemons and declared them heretics. After a swift trial, fifty Space Marines of the Chapter were burnt at the stake. Xavier Mendoza was later found dead, probably assassinated by agents of the Black Templars or the Officio Assassinorum itself.
- Lady Jena Orechiel - The daughter of an Imperial Governor and member of the Ordo Xenos, Jena is currently investigating the supposed reawakening of the C'tan. Jena is a character in the game Inquisitor.
- Velayne Ramaeus - Velayne Ramaeus is an Inquisitor of the Ordo Xenos and the leader of the faction of the Deathwatch known as the Dead Cabal.
- Gideon Ravenor - Previously an Acolyte to Gregor Eisenhorn, a more powerful psyker than even Eisenhorn himself, and author of many famous texts such as the 'Spheres of Longing'. Ravenor's early career saw him in action with Gregor Eisenhorn and together they brought down many heretics, most notably the Beldame Sadia - an accursed cybernetically-enhanced xenophile. During the Triumph under the Spacian Gate (a large parade to celebrate the Warmaster's victorious purge of the Ophidian Sub-sector) Ravenor is caught on the edge of an explosion caused by a crashing Lightning Attack Fighter. He is rendered Blind, Deaf, Mute, and senseless. Were it not for his genius and Psychic potential it would have been the end of the finest Interrogator Eisenhorn ever raised. He has been encased in a mobile life support system that serves as his protector as well as amplifying his already considerable psychic abilities. He communicates through telepathy with members of his retinue.
- Reynaard - Reynaard discovered a cult worshipping aliens on Mandall IV. Using a Deathwatch kill team, he attempted to destroy the cult, which proved to have taken over most of the capital city. After escaping, Reynaard returned with over 500,000 troops and eradicated all in the city.
- Scarn - A very secretive Inquisitor who avoids combat at all costs, and is instead a master manipulator. Last seen at an Inquisitorial Conclave six decades previously. For the past sixty years he has been working his ultimate plan, which he believes will solve all the problems that the Imperium faces, and only now are the pieces in place for stage one. Scarn was featured in the Inquisitor Campaign Supplements.
- Thaddeus - An Inquisitor of the Ordo Hereticus, he was put in charge of hunting down and destroying the renegade Soul Drinkers Space Marine Chapter. He is a rather patient man and does things slowly and concise as to do them right. He shuns other Inquisitors who use force and fear on Imperial citizens to get their information. He believes in speaking to people politely and with respect to get what he needs. He seemed to make a deal with Sarpedon, the Chapter Master of the Soul Drinkers, when Sarpedon was injured badly and held almost in death by an insanely powerful mutant attempting to gain godhood in the Warp known as Teturact. Thaddeus decided to spare Sarpedon after months of trailing the Soul Drinkers and fired on Teturact, giving Sarpedon time to finish him with the Soulspear. Thaddeus decided that Sarpedon wasn't nearly as dangerous to the Imperium as Teturact was. Thaddeus fell out of favour with the Lord Inquisitors for allowing the Soul Drinkers to continue to exist, but he still pursued them and eventually met his end facing down the Howling Griffons Space Marines after being seen as Sarpedon's ally.
- Mordecai Toth - Featured in the Dawn of War real-time strategy game. Wielder of the Daemonhammer "God-splitter", crafted from a fragment of the weapon of an Eldar Avatar of Khaine, which he later gifted to the Blood Ravens Chapter. In the Dawn of War novel series, he reclaims the "God-splitter" from the Blood Ravens, and is portrayed as a probable agent of Tzeentch, the Chaos God of Change. Toth tricked Blood Raven Captain Gabriel Angelos into freeing a powerful daemon imprisoned by the Eldar.
- Tyrus - A stanch Monodominant and hunter of all psykers who wears elaborate ornate power armour, Witchhunter Tyrus is suspicious of witches and psykers. He personally wants to kill them all, human or not.
- Amberly Vail - A member of the Ordo Xenos, she acts as the editor of the Cain Archive. It has been suggested that her relationship with Cain is more than professional.
- Commodus Voke - Ancient and famous Thorian leaning towards Monodominant save for his very powerful psychic abilities. Lived to be extremely old due to being extremely difficult to kill. Arrogant and open with his position and fame, he was a sometime ally of Eisenhorn. A legend during his time, a testament to his ability, is the fact that he fought an uncontained daemonhost in a psychic duel and was not obliterated outright.
- Black Crusade: Core Rulebook (RPG), pg. 321
- Codex: Assassin (3rd Edition)
- Codex: Daemonhunters (3rd Edition)
- Codex: Imperialis, pg. 39
- Codex: Grey Knights (5th Edition)
- Codex: Witch Hunters (3rd Edition)
- Dark Heresy: Core Rulebook (RPG)
- Dark Heresy: Ascension (RPG)
- Dark Heresy: Daemon Hunters (RPG)
- Dark Heresy: Disciples of the Dark Gods (RPG)
- Dark Heresy: The Inquisitor's Handbook (RPG)
- Dark Heresy: The Radical's Handbook (RPG)
- Deathwatch: Mark of the Xenos (RPG)
- Deathwatch: The Outer Reach (RPG), pp. 26-27
- Imperial Armour Volume Two - Space Marines and Forces of the Inquisition, pg. 192
- Imperial Armour Volume Four - The Anphelion Project
- Imperial Armour Volume Seven - The Siege of Vraks, Part Three
- Imperial Armour Volume Nine - The Badab War, Part One
- Imperial Armour Volume Ten - The Badab War, Part Two
- Inquisitor (RPG)
- Inquisitor: The Thorians Sourcebook (Specialty Game Background Book) by Gav Thorpe, pg. 24
- The Inquisition: An Illustrated Guide to the Secretive Protectors of the Imperium by Nick Kyme, Lindsey Priestley, George Stirling
- The Inquisitor Sketchbook by John Blanche
- Warhammer 40,000: Space Marine (Video Game)
- Warhammer 40,000: Rogue Trader (1st Edition)
- Warhammer 40,000: Rulebook (6th Edition)
- Warhammer 40,000: Rulebook (5th Edition)
- Warhammer 40,000: Rulebook (4th Edition)
- Warhammer Monthly 12, pg. 7
- White Dwarf 304 (UK), "
- Atlas Infernal (Novel) by Rob Sanders
- Dark Adeptus (Novel) by Ben Counter
- Ghostmaker (Novel) by Dan Abnett
- The Inquisition War (Novel) by Ian Watson. The new omnibus edition contains the trilogy Draco (previously released as Inquisitor), Harlequin and Chaos Child, as well as two interconnecting short stories.
- Maellus (Novel) by Dan Abnett