This Text is a placeholder using The Hitchhiker's Guide to the Galaxy is a comedy science fiction franchise created by Douglas Adams. Originally a 1978 radio comedy broadcast on BBC Radio 4, it was later adapted to other formats, including novels, stage shows, comic books, a 1981 TV series, a 1984 text-based computer game, and 2005 feature film.

The Hitchhiker's Guide to the Galaxy has become an international multi-media phenomenon; the novels are the most widely distributed, having been translated into more than 30 languages by 2005. The first novel, The Hitchhiker's Guide to the Galaxy (1979), has been ranked fourth on the BBC’s The Big Read poll. The sixth novel, And Another Thing, was written by Eoin Colfer with additional unpublished material by Douglas Adams. In 2017, BBC Radio 4 announced a 40th-anniversary celebration with Dirk Maggs, one of the original producers, in charge. The first of six new episodes was broadcast on 8 March 2018.

The broad narrative of Hitchhiker follows the misadventures of the last surviving man, Arthur Dent, following the demolition of the Earth by a Vogon constructor fleet to make way for a hyperspace bypass. Dent is rescued from Earth's destruction by Ford Prefect—a human-like alien writer for the eccentric, electronic travel guide The Hitchhiker's Guide to the Galaxy—by hitchhiking onto a passing Vogon spacecraft. Following his rescue, Dent explores the galaxy with Prefect and encounters Trillian, another human who had been taken from Earth (before its destruction) by the self-centred President of the Galaxy Zaphod Beeblebrox and the depressed Marvin the Paranoid Android. Certain narrative details were changed among the various adaptations.

Douglas Adams (11 March 1952 – 11 May 2001) was an English author and screenwriter, best known for The Hitchhiker's Guide to the Galaxy. Originally a 1978 BBC radio comedy, The Hitchhiker's Guide to the Galaxy developed into a "trilogy" of five books that sold more than 15 million copies in his lifetime. It was further developed into a television series, several stage plays, comics, a video game, and a 2005 feature film. Adams's contribution to UK radio is commemorated in The Radio Academy's Hall of Fame.

Adams also wrote Dirk Gently's Holistic Detective Agency (1987) and The Long Dark Tea-Time of the Soul (1988), and co-wrote The Meaning of Liff (1983), The Deeper Meaning of Liff (1990), and Last Chance to See (1990). He wrote two stories for the television series Doctor Who, co-wrote City of Death (1979), and served as script editor for its seventeenth season. He co-wrote the sketch "Patient Abuse" for the final episode of Monty Python's Flying Circus. A posthumous collection of his selected works, including the first publication of his final (unfinished) novel, was published as The Salmon of Doubt in 2002

Dirk Gently's Holistic Detective Agency is a humorous detective novel by English writer Douglas Adams, published in 1987. It is described by the author on its cover as a "thumping good detective-ghost-horror-who dunnit-time travel-romantic-musical-comedy-epic". The book was followed by a sequel, The Long Dark Tea-Time of the Soul. The recurring major characters are the eponymous Dirk Gently, his secretary Janice Pearce and Sergeant Gilks. Adams began work on another novel, The Salmon of Doubt, with the intention of publishing it as the third book in the series, but died before completing it.

A BBC Radio 4 adaptation of six episodes was broadcast from October 2007. A second series based on the sequel was broadcast from October 2008. A 2010 television adaptation for BBC Four borrowed some of the characters and some minor plot elements of the novel to create a new story, and a 2016 television adaptation for BBC America served as a continuation of the books.

There have been two television series based on Dirk Gently books and characters. The first series, Dirk Gently, featuring the character was announced during Hitchcon, a 2009 Hitchhiker's Guide to the Galaxy event to launch the sixth Hitchhiker's book. Ed Victor, a literary agent who represents Adams' estate, announced that a television adaptation of Dirk Gently's Holistic Detective Agency was in production. Stephen Mangan played Gently, with Darren Boyd as Macduff and Helen Baxendale as Susan. It was broadcast on BBC Four on 16 December 2010. The hour-long pilot was well-received, leading to three further episodes being commissioned. These aired on BBC4 during March 2012.

A second series, Dirk Gently's Holistic Detective Agency was released in January 2016. BBC America produced 18 episodes starring Samuel Barnett as Dirk Gently, Elijah Wood as Todd Brotzman, Hannah Marks as Amanda Brotzman, and Jade Eshete as Farah Black. As of July 2020 it is available on the Hulu streaming service.

Adams sent the script for the HHGG pilot radio programme to the Doctor Who production office in 1978, and was commissioned to write The Pirate Planet. He had also previously attempted to submit a potential film script, called Doctor Who and the Krikkitmen, which later became his novel Life, the Universe and Everything (which in turn became the third Hitchhiker's Guide radio series). Adams then went on to serve as script editor on the show for its seventeenth season in 1979. Altogether, he wrote three Doctor Who serials starring Tom Baker as the Fourth Doctor.

The episodes authored by Adams are some of the few that were not originally novelised, as Adams would not allow anyone else to write them and asked for a higher price than the publishers were willing to pay. Shada was later adapted as a novel by Gareth Roberts in 2012 and City of Death and The Pirate Planet by James Goss in 2015 and 2017 respectively. Elements of Shada and City of Death were reused in Adams's later novel Dirk Gently's Holistic Detective Agency, in particular, the character of Professor Chronotis. Big Finish Productions eventually remade Shada as an audio play starring Paul McGann as the Doctor. Accompanied by partially animated illustrations, it was webcast on the BBC website in 2003, and subsequently released as a two-CD set later that year. An omnibus edition of this version was broadcast on the digital radio station BBC7 on 10 December 2005. In the Doctor Who 2012 Christmas episode "The Snowmen", writer Steven Moffat was inspired by a storyline that Adams pitched called The Doctor Retires.