The Slitheen are a fictional crime family from the British science fiction television series Doctor Who. They belong to a species known as the Raxacoricofallapatorians, an alien lifeform originating from the planet Raxicoricofallapatorius. The Slitheen can disguise themselves as humans by hiding in skinsuits, though the technology they use results in them farting excessively while in disguise. The Slitheen first appeared in the first series of the show's 2005 revival in the two-part story "Aliens of London" and "World War Three", where they attempt to destroy Earth to sell its remains for profit. A single Slitheen, named Blon Fel-Fotch Pasameer-Day Slitheen (Annette Badland), escapes the subsequent destruction of the family at the end of "World War Three", and reappears later in the series in the episode "Boom Town", where she becomes Lord Mayor of Cardiff and attempts to escape the planet by destroying Earth. Subsequently, the Slitheen recur in spin-off media such as comics, books, and audio dramas in Doctor Who. They also appear as major recurring antagonists in the spin-off television series The Sarah Jane Adventures.

The Slitheen were created by Russell T Davies while writing "Aliens of London" and "World War Three", being inspired to write a crime family from various sources. They were conceived to be appealing to children and had several aspects of their character designed around this fact. The Slitheen were portrayed via physical costumes, though partially portrayed by CGI in certain shots.

During filming of their debut episodes, Davies was impressed by the performance of Badland as Blon resulting in Davies bringing her back for "Boom Town" to portray Blon following the events of the two-parter. Subsequently, Davies pitched the concept for spin-off series The Sarah Jane Adventures with the idea of Sarah Jane Smith fighting the Slitheen. This inclusion was cited to be because they were popular with children and would help attract viewers of Doctor Who to The Sarah Jane Adventures. The Slitheen were initially criticised by critics, with many disliking the childish humor and lack of narrative weight they were treated with, however Blon's return in "Boom Town" was highlighted for providing greater depth to the family, with their later character depth receiving analysis. The feasibility of the family in real life has also been explored and analysed.

Doctor Who is a long-running British science-fiction television series that began in 1963. It stars its protagonist, The Doctor, an alien who travels through time and space in a ship known as the TARDIS, as well as their travelling companions. When the Doctor dies, they are able to undergo a process known as "regeneration", completely changing the Doctor's appearance and personality. Throughout their travels, the Doctor often comes into conflict with various alien species and antagonists.

The Slitheen are a criminal family of Raxicoricofallapatorians, a species who hail from the planet Raxicoricofallapatorius. They are capable of disguising themselves as humans via skin suits, but the process causes a buildup of "gas exchange", causing the Slitheen to fart while in disguise. They are susceptible to vinegar due to being calcium-based lifeforms, causing them to explode on contact with vinegar.

The Slitheen first appear in the 2005 episodes "Aliens of London" and "World War Three". In the episodes, the Slitheen have infiltrated the Government of the United Kingdom, replacing many key political figures. They crash a spaceship, piloted by a pig, into Big Ben, causing a state of world panic. The family wished to use this paranoia to allow the United Nations to let the government utilise its nuclear arsenal against a supposed alien threat; with this nuclear arsenal, the Slitheen will destroy the planet, selling the leftover chunks as spaceship fuel. The Ninth Doctor and his allies are able to arrange for a Harpoon missile to demolish 10 Downing Street, killing all of the Slitheen and averting the crisis.

A single Slitheen from the invasion survived. Appearing in the 2005 episode "Boom Town", Blon Fel-Fotch Pasameer-Day Slitheen assumed the identity of Margaret Blaine of MI5, and slowly worked her way up to the position of Lord Mayor of Cardiff. Blon planned to channel nuclear power into an alien device, which would allow her to escape the planet at the cost of the planet's destruction. Blon cornered the Ninth Doctor and his allies in the TARDIS, at which point she was exposed to the "heart" of the ship. This reverted her back to an egg, which the Doctor took back to her home planet so she could have a chance at a peaceful life. Following this, a Slitheen appeared in the 2005 mini-episode "Attack of the Graske", in which one is captured by an alien called a Graske. It is released from its prison and attacks the Graske.

The Slitheen would appear in several pieces of spin-off media for the series. They appear in the novel The Monsters Inside, in which a pair of them ally with the Doctor to help stop an invasion attempt by the Blathereen. The 2009 novel The Slitheen Excursion depicts the Tenth Doctor attempting to foil a Slitheen plot in ancient Rome. Big Finish audio dramas Death on the Mile and The Taste of Death see further plots by the Slitheen, with the former being thwarted by the Doctor's friend Lady Christina de Souza, while the latter is stopped by the Tenth Doctor.