The Inquisition is a clandestine organization that investigates and eliminates the various threats against the Imperium of Man. Created by Malcador the Sigilate, the Inquisition was originally created to stop Chaos during the Horus Heresy. However, their mission expanded as new threats emerged, and various Ordos were developed. An individual Inquisitor has the power to requisition any military assets he needs for his mission, and can order for Exterminatus of any planet deemed too dangerous to allow to exist. They can also call upon various agents at their disposal, whether they be personal henchmen, the members of the Officio Assassinorum, or chambers militant of the main Ordos.
In practice, many Inquisitors are far from the most reliable agents, especially those that spend too much time dealing with Chaos. Many will opt for the "better safe than sorry" approach and destroy or forcibly sterilize entire populations based on rumors, and noncomformance with mainstream Imperial Society can also be interpreted as Heresy. Thus they are identified as one of the key reasons behind the Imperium's decay, along with the existence of the Ecclesiarchy and the corruption of Imperial bureaucrats.
Inquisitors can be divided into two general camps: Puritans, and Radicals. The Puritans are by-the-book and enforce Imperial dogma to the letter, though they can be extremely fundamentalist, leading to decay, misery, and carpal tunnel from excessive use of exterminatus On the flip side, Radicals deviate from Imperial doctrine and will frequently turn to extreme methods to solve problems, including using Chaos weapons or rituals, which will oftentimes lead to the inquisitor's direct corruption, or they lose control of whatever daemon or artifact is in their possession. Thus Radicals are viewed as borderline heretics.
The main Ordos of the Inquisition are:
- The Ordo Mallaeus, charged with hunting Daemons. They are supported by the Grey Knights.
- The Ordo Hereticus, charged with rooting out heretics. They are supported by the Sisters of Battle.
- The Ordo Xenos, charged with eliminating Xenos. They are supported by the Deathwatch.