The Ruler of the Universe, also known as the Man in the Shack, is a man on a planet inside a improbability field. The Ruler of the Universe believes that the past is "a fiction designed to account for the discrepancy between my immediate physical sensations and my state of mind".

He lives in a shack with his cat, whom he calls "the Lord". He appears very deferential and largely uncertain on almost every front. He believes nothing unless he can prove it by seeing it himself.

He was visited by Zaphod Beeblebrox, Trillian, Zarniwoop, and in some versions of the story, Arthur Dent and Ford Prefect, as Zarniwoop wanted to ask him some questions.