|“||Well, Zaphod's just ziz guy, you know?||„|
|~ Gag Halfrunt's catchphrase|
He is the one who put the forms for the destruction of Earth (under the pretense of it being used for a hyperspace bypass) in the Alpha Centauri offices some 50 years ago. He orders the destruction of the Earth and employs Vogon Jeltz to do the job. This is successful.
But two humans survive - Tricia McMillan and Arthur Dent. This annoys Halfrunt, because he believes they still have the Question fitting the Ultimate Answer in their brains. Halfrunt contacts Jeltz on his ship to gun the Golden Heart - the spaceship upon which the two humans have found refuge - down in orbit and kill them all, but this is unsuccessful due to Zaphod Beeblebrox having a séance and contacting his dead grandfather to save them.
Then Halfrunt employs the Vogons to infiltrate the Hitchhiker's Guide offices and turn the book into an evil corporation to find all Earths in every universe. This is done, the Guide is taken over and a new edition of the Handbook created capable of operating in many different universes at once.
Halfrunt also uses a man named Zarniwoop to lead the Vogons, asking him to get Ford Prefect as their agent, but Ford flatly refuses. Then Halfrunt is ultimately successful when, despite Ford bankrupting his company, he finally tracks Arthur and Ford and Tricia down on another Earth, and - manipulating Grebulonian warriors to do his dirty work - destroys it, ending all hope of matching the Ultimate Answer to the proper question.
Halfrunt, being a leading psychiatrist, fostered similar ideas to ancient philosophers Vroomfondle and Magicthise - it is improper for a machine to resolve the ultimate questions about existence, mainly because it would make all human (or human-ish) thinkers obsolete and unemployed instantly. He might also have been concerned that if the Ultimate Answer and the Ultimate Question were known in the same universe at the same time, the universe might cease to exist "to be replaced by something even more incomprehensible".
Halfrunt made a cameo in the 2005 movie adaptation being portrayed by Jason Schwartzman (although uncredited) who would later portray Gideon Gordon Graves. He appears while Zaphod is watching a news channel talking about himself on the TV. Just before Trillian turns the TV off an interview feature Halfrunt is seen when he says his famous catchphrase. He also has an American accent in the movie and appears a lot younger and less scruffy than his previous counterparts.