From a barren planet, Inquisitor hunt down heretics, and have them brought to the Citadel. None of these heretics are ever heard from again.
Inquisitors use a variety of weapons and are backed up by their extremely disciplined Inquisitor Troopers. They often work alone, except when taking control of Justiciar field units for their own purposes. Officially, they are under the chain of command. Unofficially, they follow no one's orders but their Grand Inquisitor.