Zarniwoop, introduced as an executive of the Hitchhiker's Guide to the Galaxy, is in fact one of a number of people who entered into a conspiracy to discover who actually ruled the universe. Another member of this conspiracy was Zaphod Beeblebrox.
After Zaphod stole the Heart of Gold and experienced the adventures of the Primary Phase, he received a message from himself in a dream, "Go see Zarniwoop". He headed to Ursa Minor Beta to meet him at the headquarters of the Guide. Entering Zarniwoop's office, he stepped into an electronically generated universe, designed expressly to keep him safe.
Beeblebrox and Zarniwoop met up in the artificial universe (after Zaphod had several adventures in it) and headed for the planet that presumably housed the Ruler of the Universe. Zarniwoop was marooned there; by the entire group of heroes in the book series, by Arthur Dent alone in the radio series (leaving Zaphod and Ford Prefect with Zarniwoop).