The Hitchhiker's Guide to the Galaxy (in-universe)

The Hitchhiker's Guide to the Galaxy was a series of books from the 20th century that was referenced by the Doctor on a few occasions. The Doctor once asked, rhetorically, who had said that "Earthmen rarely invite their ancestors to dinner", which comes from the series. (DW: Ghost Light) The Doctor once compared himself to Arthur Dent after saving the Earth from invasion in a dressing gown (Dent's trademark dress), and after being awoken from his post-regenerative coma by tea, the character's favourite drink. (DW: The Christmas Invasion) The number 42, which in the Hitchhiker's books was the answer to the question of life, the universe, and everything, was one of the numbers the Doctor guessed when trying to find out the security protocol for the the Host. (DW: Voyage of the Damned) Also, the Doctor had used the phrase "DON'T PANIC"--the exact words on the cover of the Guide in "big, friendly letters"--very expressively when in a tight situation in an episode written by Douglas Adams, himself. (DW: The Pirate Planet)

Real World connections
Hitchhikers creator Douglas Adams wrote a number of Doctor Who serials and served as its script editor during Season 17. Consequently, lines from Hitchhiker's Guide found their way into The Pirate Planet, while Hitchhiker's character Oolon Coluphid gets a mention in Destiny of the Daleks, which Adams script-edited (the Doctor is seen reading one of Caluphid's books, Origins of the Universe. Shada, also written by Douglas Adams, involves a Ford Prefect car. The storyline of Adams' Life, the Universe and Everything was based on a rejected Doctor Who script called Doctor Who and the Krikkitmen.


 * See Douglas Adams

Just prior to becoming the Doctor, Peter Davison made a cameo appearance in the BBC's 1981 adaptation of the first book as the "Dish of the Day". His wife, Sandra Dickinson, played Trillian in the miniseries.

Bill Nighy, who played a role in the 2005 film, was seriously considered for the role of the Ninth Doctor, Tenth Doctor and the Eleventh Doctor, he expressed interest in all three roles. Stephen Fry, an actor with some connection to the Who franchise, narrated the film.

The number 42, made famous in the series, was given a nod by Doctor Who when it was used as the title for an episode during Series 3.

Metafictional parallels and references

 * The plot of Voyage of the Damned is similar (but not identical) to that of "Starship Titanic", a video game authored by Adams which was published in 1998. Both feature a large luxury spaceship/cruiseliner named "Titanic" which goes out of control and whose computers must be manipulated to fix the ship. The video game was based on a brief mention of the ship in the first Guide book, which was unable to send out its first and only message - an S.O.S. - during its launch before suffering a "total existence failure".
 * 42 shares its title with the Answer to Life, the Universe, and Everything, as revealed in Adams' Hitchhiker's series. As with the spaceship stolen by Arthur Dent and friends in The Restaurant at the End of the Universe, the ship in 42 is on its way to crashing into a star, leaving its passengers with no escape.
 * The reference to Oolon Coluphid has raised speculation as to whether the Doctor Who Universe and that of the Hitchhiker's Guide are one and the same. The BBC's viral marketing website Defending the Earth! included a forum posting by a man named Arthur Dent who wrote, "This rather odd man was lying down in front of a bulldozer in front of my home." Another matter blurring the lines between the Hitchhiker's universe and the Whoniverse is the Tenth Doctor's early reference to Arthur Dent being a "nice man" who saved the universe in "his jim-jams"; it's left ambiguous as to whether he's referring to a fictional character or a real person. (DW: The Christmas Invasion)
 * Perhaps by a coincidence, the scene in the third book of the quintilogy (later adapted into a radio script of the same name) Life, the Universe, and Everything, in which Arthur Dent and Ford Prefect, materialise in Lord's Cricket Ground, is similar to a similar scene in The Daleks' Master Plan in which the Doctor materialised his TARDIS at The Oval.
 * On the second disk of The Hitch Hikers Guide to the Galaxy, during the opening credits you can see the TARDIS there.
 * One of the spaceships in BBCR:Max Warp is described as a "Lazlar Lyricon custom job". This is how one of the spaceships in the Milliways car park in episode 5 of HHGG was described.