1. Someone who asks a succession of relentless and searching or even hostile questions: Rufus, the investigative journalist, was known as a tough inquisitor because he was sometimes asking too many personal questions during his interviews.
2. When capitalized, Inquisitor refers to someone who was an official working for the Roman Catholic Inquisition: The Inquisitor was cruel and unpopular and so the people in the streets spoke angrily and threatened to revolt.