"No spawn of Hell can hide from the gaze of the Inquisitor, no matter what form it takes."(src)
Inquisitors are a type of enforcer found in many organizations across Sanctuary's history.
Groups that utilized Inquisitors include(d) the following:
Cathedral of LightEdit
Inquisitors were present in the Templar Order. They were responsible for the initiation of new Templars into the order through means of torturing them in order to "cleanse" them of their "sins" and remove the memories of who they were before they joined the order.
Templar Order Inquisitors are fought in "The Templar's Reckoning" follower quest in Templar Outpost. They are identical to Westmarch Soldiers in terms of abilities, and are armed either with spears or with crossbows.