The planet of Golgafrincham was once home to the Great Circling Poets of Arium. The descendents of these poets made up tales of impending doom about the planet. The tales varied; some said it was going to crash into the sun, or the moon was going to crash into the planet. Others said the planet was to be invaded by twelve-foot piranha bees, and still others said it was in danger of beaing eaten by an enormous mutant star goat.
These tales of impending doom allowed the Golgafrinchans to rid themselves of an entire useless third of their population. The story was that they would build three Ark ships. Into the A ship would go all the leaders and scientists, and other achievers. Into the C ship were supposed to the people who made things and did things, and into the B ark would go everyone else, such as hairdressers and telephone sanitizers. They sent the B ship off first, but of course the other two-thirds of the population stayed on the planet and lived full, rich, and happy lives until they were all ironically wiped out by a virulent disease contracted from a dirty telephone.
The 'B' Ark had a captain who spent all his time in the bath, and two security guards--the overly-militant Number Two and the mellower Number One. It was onto this ship that Arthur Dent and Ford Prefect found themselves after escaping from the Disaster Areas stuntship (a Haggunneon battle cruiser in the radio series). The ship was programmed to crash-land on their destination planet, which Ford and Arthur discover is prehistoric Earth when they find the signature of Slartibartfast, the Magrathea coastline desginer, on a glacier in what would become Norway.