An Inquisitor was a rank held by officers within the Imperial Starfleet of the Terran Empire in the mirror universe.
Deanna Troi held the rank of Inquisitor on the ISS Stargazer under the command of Captain Jean-Luc Picard during the years when the Empire had fallen to the Klingon-Cardassian Alliance. (TNG comic: "Mirror Broken, Issue 1")