As a psychiatrist, Halfrunt realised that should the Ultimate Question to Life, the Universe, and Everything ever be found, the psychiatric profession would lose the business of many bewildered and highly profitable clientele. Therefore, it was Halfrunt that ordered and paid the Vogons to demolish the Earth (under the premise of building a hyperspace bypass). Following that, he had Jeltz hunt down the Heart of Gold and attempt to destroy it. Believing that Arthur Dent and Trillian (the last two members of Earth's original programming) were killed, he returned to his profitable business.
While the crew of the Heart of Gold survived that attack, Halfrunt's order eventually led to the destruction of Earth anyway, due to the Vogon's paranioa with finishing the job, the Earth was finally destroyed, under the watchful eye of the Vogons by the Grebulons.
Gag Halfrunt appears in the Douglas Adams book The Restaurant at the End of the Universe in a sub-etha radio interview with a heavy accent. He also appears in the 2005 film The Hitchhiker's Guide to the Galaxy.