Ford is a good friend of the main character, an ordinary Earthman named Arthur Dent, who has known him for several years and believes him to be from the town of Guildford in Surrey. However, he is actually an alien from a small planet in the vicinity of Betelgeuse, and had originally only come to Earth to do some research for an article he was writing on it for the Guide.
Although Ford had taken great care to blend into Earth society, he had "skimped a bit on his preparatory research", and thought that the name "Ford Prefect" would be "nicely inconspicuous".
In fact, the Ford Prefect is a type of car, although author Douglas Adams later observed that the joke was lost on U.S audiences who assumed it was a joke on "perfect". Adams explained in an interview[1] that Ford "had simply mistaken the dominant life form", although some commentators believe this explanation to be apocryphal, or at least wildly inaccurate.
Ford came to Earth for a week, and got stuck there for fifteen years, departing only when a fleet of Vogon construction ships appear in the first episode, taking Arthur Dent with him. For the listener/reader/viewer, Ford is the source of much explanation of the weird universe that Arthur finds himself in, for example the importance of knowing where your towel is, sticking fish in your ear, and why the greatest cooks in the universe cook such bad food on Vogon spaceships.
In the novel, we are told that Ford's original name is "only pronuncible in an obscure Betelgeusian dialect" which was almost wiped out by the "Great Collapsing Hrung Disaster of Gal./Sid./Year 03758", a mysterious catastrophe which took place on the planet of Betelgeuse Seven and which Ford's father was the only man to survive. Ford never learned to pronounce his original name. At school, he was nicknamed "Ix", which translates as "boy who is not able satisfactorily to explain what a Hrung is, nor why it should choose to collapse on Betelgeuse Seven".
Despite all this, his semi-cousin Zaphod Beeblebrox calls him "Ford" the first time they are reunited. Douglas Adams has explained this by indicating that, prior to visiting Earth, Ford went back in time and changed his name at birth to Ford Prefect; hence he has now always been called Ford.
In the original radio series Ford was played by Geoffrey McGivern. On television he was played by David Dixon.