Gag Halfrunt

In the series, he is the private braincare specialist of Zaphod Beeblebrox, and is not a major character in terms of the amount of dialogue or prominence he gets. However, he is major in the sense that the entire plot loosely revolves around him (at least in the radio series version of HHGG). However, this may be in part due to the fact that large parts of the series were made up by Adams as he went along, and some of the plot developments and explanations were more a way to tie up some of the glaring loose ends than part of a predetermined master plan.

In the story, Zaphod and Gag Halfrunt (as leader of a group of psychiatrists) are in cahoots to discover who or what is REALLY running the universe. Because the Earth is really a giant computer built to determine the very same thing, the psychiatrists cannot afford to have the answer revealed, because this would put them out of a job (on the rather weak premise that if the answer becomes known, everyone would suddenly start leading happy and productive lives, rendering shrinks unnecessary). Therefore they hire the Vogons to destroy the Earth to prevent the answer being discovered. Later the Vogons also try (under Gag's direction) to destroy the starship Heart of Gold because it is carrying Arthur Dent, who may have the answer buried in his brain somewhere. All of this is unknown to Zaphod because he has brainwashed himself to forget about the collusion (though again this seems to be more of a device to explain why it only becomes clear towards the end of the second series and hasn't been mentioned before). In the end Zaphod "remembers" and does in fact, discover who is really running things - some guy in a shed.