The Golgafrinchans were a race of Humans from planet Golgafrincham. They were known for being naive and frivolous even by Human standards and for often having dangerously thin bowel walls which are prone to rupturing.
A descendant of the Great Circling Poets of Arium invented spurious tales of their planet's impending doom, such as twelve-foot Piranha Bees or an enormous mutant star goat. These enabled the people of Golgafrincham to rid themselves of an entire useless third of their population - hairdressers, jingle writers, telephone sanitizers, and the like - under the pretense of locating a less doomed planet. The other two-thirds stayed firmly at home and lived full, rich and happy lives until they were all suddenly wiped out by a virulent disease contracted from a dirty telephone.
In the meantime, the useless Golgafrinchans crash-landed on Earth, where the indigenous dominant race took a long look at them and lost the will to live. They are the primary ancestors of modern Earthlings, which sadly explains a lot.