It is several millennium hence. Mankind has spread across the stars and the Empire of Man has conquered the galaxy. At the head of the Empire is the God_Emperor of Mankind. He remains on Earth, a symbol of devotion and faith. But not all is gumdrops and sunshine. In its conquest of the galaxy, Mankind has found numerous alien empires, and far worse things. Having discovered hyper-light speed travel, Man has discovered an alternate dimension, known as the Curse. It is a repository for all conscious thoughts and emotions and from these baleful energies pour forth demons that tear at the fabric of reality, intent on devouring the souls of the living after corrupting human hosts. And, as was always true of any civilization, there are dissenters among the Empire. There are those who traffic with the forces bent on humanity's eradication, willingly manifesting demons, or committing blasphemy against the Imperial Creed, disavowing worship of the God-Emperor for far darker powers. In these dark, troubled times, the Inquisition was created.
The Inquisition is a clandestine organization whose sole mission is the preservation of Mankind's dominion over the stars. It is divided into three separate branches: the Ordo Xenos, the Ordo Malleus, and the Ordo Hereticus. The Ordo Xenos is tasked with the extermination of all aliens and their traces fromt he galaxy. The Ordo Malleus fights the never-ending battle against the creatures of the Cursed Realm and their followers. The Ordo Hereticus seeks out all cults and heretics who jeopardize the authority of the Imperial Creed.
An Inquisitor's power is limitless, his scope unrestrained. Cities may burn, populations executed, whole planets and systems rendered barren wastes; all at the behest of an Inquisitor. He has access to all resources, can usurp any power, execute anyone if he believes that it will further his mission. For the Inquisition is the God-Emperor's will incarnate and each Inquisitor is a vessel for his holy wrath. They are everywhere and nowhere; all Imperial citizens, from the lowest scribe to the Lords of Earth themselves fear them, for none are above the scrutiny of the Inquisition.
Ordo Xenos
The Ordo Xenos is the branch of the Emperor's Holy Inquisition that is entirely devoted to hunting down and destroying alien life. Though Inquisitors are held in awe and terror across the Imperium, it is the alien and thos who dare to arbor it that need fear the focused wrath of the alien hunter. Equipped with the best wargear the Imperium can supply, possessed of extensive knowledge of their foe adn blessed with a fiery hatred, the Ordo Xenos is the first and greatest of Mankind's defences against the alien. When the xenos taint is subtle, the Ordo's Inquisitors will cut it out with scalpel-sharp vigilance and determination. When the alien comes on in a great horde, the Deathwatch, elite warriors taken from among the Chapters of Space Marines, will meet it head to head an purge it with fire and steel.
Motto:
"Suffer not the alien to live!"
Ordo Malleus
Meaning the Order of the Hammer in the High Gothic tongue, the Ordo Malleus is the division of the Emperor's Holy Inquisition concerned with destroying the physical manifestation of the Cursed Realm itself: the Demon. Its members have pledged their every waking hour to the discovery and destruction of the demonic wherever it is to be found. It is their role to hunt out and purge those who consort with the demon and the hideous things they conjure before their blasphemous actions give rise to full-scale demonic invasions.
Such is the authority of an Inquisitor and the magnitude of the threat posed by the Demonic, that no sacrifice is too great to combat this menace, and no force too strong to bring to bear against the horrific sevants of the Curse. Even in victory those who have fought alongside a Demonhunter may well be subsequently exterminated to prevent the taint of the Curse spreading further: Space Marines, too valuable to simply execute, are usually mind-scrubbed to eradicate the taint of the Curse, which can corrupt even the most faithful.
But there are times when the demon bursts from the aether in such numbers that the Inquisitors of the Ordo Malleus need to call upon their own Chamber Militant- warriors even more powerful and devout than the Space Marines- to triumph. Times when ravening monstrosities pour into the material dimension in a gibbering tiede, hungry for the souls of the innocent. Only one force in the galaxy has any chance of stemming such a demonic infestation- the Grey Knights.
Motto:
"Banish the Cursed!"
Ordo Hereticus
At the end of the Age of Apostasy, the Inquisition formed a secret order within its ranks to watch the Ecclesiarchy more closely. While the Inquisition as a whole monitors every aspect of the Imperium, the Ordo Hereticus is primarily concerned that another Plague of Unbelief does not occur. Though the Ecclesiarchy regulates itself and its followers closely (primarily with the Adepta Sororitas), the Ordo Hereticus provides another line of defenceto ensure that those in power within the Ecclesiarchy do not abuse their position to such an extentthat it threatens the stability of the Imperium again. These Inquisitors watch Wars of Faith closely to ensure the objectives laid down by the Ecclesiarch are both justified and not exceeded by those actually fighting. They monitor the Frateris Militia to safeguard the spirit of the Decree Passive (if not its letter) and to ensure its prohibitions stay enforced. They also regulate the amount of wealth and territory claimed by individuals within the Ecclesiarchy and halt attempts by Cardinals trying to amass more power than the Ordo Hereticus deems appropriate.
Motto:
"Burn the Heretic, that He does not harm the Pure!"
*for further history of these matters and references, one must have a working knowledge of Warhammer 40,000. (Copyright Games Workshop Ltd., London, UK.)
**all material is, for the most part, directly used from literature published by Games Workshop. I take no credit except for small changes to keep it concurrent to my own story.