Inquisitor

The Inquisitors are agents of the collective organization known as The Holy Orders of the Emperor's Inquisition. Although they have various methodologies and can belong to different Ordos, they ultimateley serve the Emperor and the Imperium of Man (the intergalactic empire of mankind in the 41st millennium).

Who can be an Inquisitor?
There is no specific background that is required for an Inquisitor, as anyone who shows talent, can be recruited by other Inquisitors, for instance. Most of the best Inquisitors come from the Schola Progenium, an academic environment where orphans are indoctrinated at an early age.

Duties
Most importantly: they serve the Emperor, they investigate and deal with potential threats to the Imperium and humanity. This can be a physical threat, such as enemies of the Imperium, but it can be a moral threat, such as heresy (treasons of thought and faith, or an act against the ways and creed of the Imperium).

Kinds of Inquisitors
There are multiple Inquisitorial Ordos who deal with different kinds of threats. The major ones are Ordo Malleus (against daemonic threats), Ordo Hereticus (against heresy), and Ordo Xenos (against alien forces). In a different approach, there are puritan and radical Inquisitors who will use different kinds of resources against the threats to the Imperium. They show variety in their equipment and abilities: there are excellent fighters, who aren't afraid of gearing up with the heavy equipment and deal some damage themselves, and there are some Inquisitors who have the ability to use psychic powers (psykers). There is no "official" restriction of how they operate as long as they serve the Imperium effectively.

Superiors and subordinates
Experienced Inquisitors can declare that they serve the Emperor directly and have unlimited authority. They aren't required to belong to a specific Ordo, but in most cases, they do. They can be accompanied by a group of acolytes who are servants and effective agents in the Inquisition.