The Golgafrinchans were a race of humanoid beings who realised that there were three types of beings on the planet of Golgafrincham. Thinkers, Workers, and the strange Middle Class.
The middle class comprised of hairdressers, lawyers, telephone sanitisers, and other such "worthless jobs."
The Thinkers built a ship and convinced this third, middle class to leave Golgafrincham by telling them several different reasons, including: that the planet was going to crash into the sun (or perhaps the moon was going to crash into the planet), that the planet was being invaded by a gigantic swarm of twelve foot piranha bees, and that "the entire planet was in imminent danger of being eaten by an enormous mutant star goat".
The middle class was sent off, told that the other Golgafrinchans would follow soon, however they remained on the planet with no intention of leaving. The Third class ended up on Earth, "mucking up the program to determine the ultimate question" while the rest of the classes were killed off by a raging disease contracted from public telephones.