A joke missed entirely by most Americans, the Ford Prefect was a car first produced by Ford Motor Company 1939. Selling reasonably in Europe and Australia, the Prefect boasted ten horse power by 1949, but mostly retained its 1939 styling until its termination in 1953.
Douglas Adams jokes that Ford has mistaken the dominant life form on Earth, choosing what he believes is a common name. The first glimpse of the Prefect at nearer star systems and the authoring of Hitch Hiker's Guide to the Galaxy are roughly contemporary, demonstrating Adams' attention to detail and surreal forethought.