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

The Hitchhiker's Guide to the Galaxy was a 20th century radio play-turned-series of novels by Douglas Adams that was referenced by the Doctor on a few occasions.

Real World connections

 * Hichhikers 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 Hitchiker's character Oolon Coluphid gets a mention in Destiny of the Daleks, which Adams script-edited. Unfortunately, Adams' three teleplays for Doctor Who were some of the only ones never adapted as novels by Target Books.
 * The storyline of Adams' Life, the Universe and Everything was based on a rejected Doctor Who script called Doctor Who and the Krikkitmen.
 * 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.

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. Whether the similarity is intentional or coincidental is unknown. 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, revealed in the eponymous book written by Adams, the third volume in the 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. This is unlikely as Arthur Dent is a 20th century human who witnesses the destruction of his planet in the first book; the Whoniverse establishes that Earth survives more or less intact until the year 5 billion (although there are instances in The Hitchhiker's Guide, as in Doctor Who, where events are rewritten). A more likely scenario is there happens to be an author named Oolon Coluphid in both universes. That said, 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". (DW: The Christmas Invasion)
 * Perhaps by a coincidence, the scene in the third book of the quintilogy (based on the 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 in the same stadium.