Ford Prefect

In the film, Ford is played by Yasiin Bey, credited as Mos Def. He shows up while Arthur is lying in front of the bulldozers, distracts the workers with beer and takes his friend to the pub to tell him the truth: he's an alien, a researcher for the Guide, and the Vogons are destroying Earth that very day.

Ford gets them both a ride on the Vogon ship. After the poetry reading, they're thrown into space and saved by the Heart of Gold, captained by Zaphod Beeblebrox, Ford's relative. The rescue is so unlikely that it only happens thanks to the ship's Infinite Improbability Drive.

On the Heart of Gold, Ford follows Zaphod in the search for Magrathea and helps rescue Trillian on the Vogon homeworld. On Magrathea, he, Zaphod and Trillian meet the computer Deep Thought and learn that Earth was a bigger computer built to find the Question.

Later, Ford is at a dinner with the others and two mice, the same ones who commissioned Earth and now want Arthur's brain. When the Vogons surround the group, Marvin handles it, and Ford heads off with his friends for the Restaurant at the End of the Universe.

In the BBC series, Ford is David Dixon, who replaced Geoffrey McGivern, the radio Ford. The story of Earth, the Vogons and Magrathea plays out again, until an explosion sends the group to Milliways, the restaurant at the end of the universe, where Marvin has been waiting for them for ages.

There, Ford and Zaphod talk Marvin, now a car park attendant, into helping them steal a ship belonging to the band Disaster Area. The catch: it's set to dive into a sun.

Ford and Arthur teleport out and land on prehistoric Earth, aboard a ship of frozen Golgafrinchans, the workers deemed useless who were tricked into leaving their own planet.

Ford is the one who works out what that means: these passengers, not the cave dwellers, will become the human race. The Question Arthur pulls from Scrabble tiles comes out garbled, a sign that Earth's program went wrong. The series ends with the two of them stuck in that past.

In Douglas Adams's books, Ford is with Arthur from the first volume on and returns in Eoin Colfer's And Another Thing.... On the radio he was Geoffrey McGivern; in the 1981 series, David Dixon; in the 2005 film, Yasiin Bey.