|Doctor Who alien|
|Type||Living calcium bipeds|
|Affiliated with||Various (families)|
|First appearance||"Aliens of London"|
|Last appearance||"The Nightmare Man" (The Sarah Jane Adventures)
"The End of Time" (cameo)
The Slitheen are a family of massive, bipedal extraterrestrials from the British science fiction television series Doctor Who and are adversaries of the Doctor. They first appeared in the 2005 series episodes "Aliens of London" and "World War Three", and subsequently recur in later episodes of both Doctor Who and spin-off series The Sarah Jane Adventures. They are creatures of living calcium, hatched from eggs and native to the planet Raxacoricofallapatorius. Though the name "Slitheen" refers to a specific family, the term has been used by the Doctor and Rose to refer to the Raxacoricofallapatorian race in general.
The Slitheen are a ruthless criminal sect whose main motivation is profit. They are instinctive hunters, being trained to hunt and kill from as young as twelve. The members of the family are convicted criminals on their planet, subject to the death penalty if captured. Blond (the last of the slitheen family on earth) had a second chance to relive her life thanks to the 9th Doctor.
Physical characteristics 
Raxacoricofallapatorians are eight feet tall, rather fat with long forearms and powerful claws. They do not appear to have eyelids, but have a nictitating membrane. They have a highly-developed sense of smell, able to track a single target across a few city blocks, smell adrenaline and hormones in people, and can sense if one of their own dies. Female Raxacoricofallapatorians can produce poisons within their bodies which they then use against their enemies. Known methods of delivery include a poisoned dart that is formed in the finger and then fired and exhalation of poisoned breath. Members of the Slitheen family have green skin, though there is variation in the skin tone of other Raxacoricofallapatorian families. In The Sarah Jane Adventures episode, The Gift, members of the Slitheen-Blathereen family group are seen to have orange skin.
The Slitheen disguise themselves by fitting into the skins of their victims, using compression fields created by a collar worn around their necks to squeeze their huge size into a slightly smaller space. Initially the compression ratio was limited, so the disguises tended to be that of obese people. This issue was overcome by new technology by the time of The Lost Boy in which the skins of thinner people were used (by the time of From Raxacoricofallapatorius with Love short people could also be used). The exchange of gases that compression entails also builds up within the acquired skin, causing a very loud fart in humans (the expelled gas smells like bad breath, which the Doctor noted was a form of calcium decay, although in reality the bacteria that cause tooth decay are different from those that cause bad breath). This side-effect is also overcome by the newer technology in The Lost Boy.
Gas exchange 
When the Slitheen are in their skin suits they fart loudly; they call this the gas exchange. This can also be caused by over-eating. In "The Gift" (Sarah Jane Adventures) Sarah Jane and the gang destroy the food,a plant called Rakweed, which is native to Raxacoricofallapatorius, in the stomachs of the Blathereen, which produced methane gas.
Raxacoricofallapatorians are vulnerable to acetic acid, which reacts explosively—and fatally—with their bodies, which makes Slitheen allergic to vinegar, ketchup and Coca-Cola. One of the Raxacoricofallapatorian methods of execution is the lowering of the condemned into a cauldron of acetic acid, which is then heated to boiling. The acidity of the solution is formulated to dissolve the skin, allowing the internal organs to drop into the liquid while the condemned is still alive, reducing them to "soup" and resulting in a slow and painful death. In "World War Three", when a single Slitheen was electrocuted, the effects were transmitted to other Slitheen, even those across the city.
When they first appeared in "Aliens of London" (set in 2006), the Slitheen had been in Great Britain for some time, having infiltrated various levels of British society, from community leaders and military personnel to mid-level politicians and government officials. Their intent was to instigate World War III and sell the radioactive remains of Earth to a depressed galactic economy as fuel for interstellar spacecraft. They staged the crash landing of an alien spaceship in central London, staging a cybernetically augmented pig as an "extraterrestrial" body.
With the world in a state of heightened alert and panic, and with one of their number assuming the role of Acting Prime Minister, they persuaded the United Nations to allow the United Kingdom to use its nuclear arsenal against the alien "massive weapons of destruction". Before the Slitheen could receive the launch codes, the Ninth Doctor arranged for a Harpoon missile to demolish 10 Downing Street, ending the scheme and killing all but one of them who managed to escape through an emergency teleport.
Blon Fel-Fotch Pasameer-Day Slitheen, who had assumed the identity of Margaret Blaine of MI5, survived and appeared in the episode "Boom Town". In the intervening six months, "Blaine" was elected as Lord Mayor of Cardiff and planned to leave Earth by using the energy from a new nuclear power station to interact with the Cardiff Rift, unconcerned that the planet would be destroyed in the process. Blon was stopped by the Doctor and his companions, and on exposure to the "heart" of the TARDIS, regressed to an egg. The Doctor took the egg to the hatcheries on Raxacoricofallapatorius so she could be given a second chance at life.
Some years after the events of "World War Three", in Revenge of the Slitheen (set in either 2008 or 2009) another group of Slitheen infiltrated a construction company with plans to turn off the Sun and destroy Earth by draining the world's energy. It is mentioned that the Judoon have begun to force out the Slitheen, and the various other families have been working against them. The families Blathereen and Hostrazeen are mentioned to be part of the Raxacoricofallapatorian ruling bodies, the Senate and the Grand Council. After the Commander was killed by Maria Jackson, Luke Smith was able to trick the Slitheen into resetting their machinery, which then malfunctioned and exploded. Two of the remaining Slitheen were killed, and the others escaped, including Korst the first child Slitheen to appear, who later returned.
The Slitheen returned in The Lost Boy where, using the newer compression technology, two posed as Luke's 'real' parents. They were under the command of Korst from Revenge of the Slitheen, who planned to avenge the deaths of his family. Another shorter adult Slitheen appeared in the 2009 From Raxacoricofallapatorius with Love, masquerading as a galactic diplomat in an attempt to steal Sarah Jane's robot dog K-9.
The Slitheen appeared in the New Series Adventures novel The Monsters Inside by Stephen Cole. When the Ninth Doctor and Rose are arrested in the Justicia System in the year 2501, the Doctor shares a cell with Dram Fel-Fotch and Ecktosca Fel-Fotch Happen-Bar Slitheen, who claim that after the Earth incident, the remnants of the family went bankrupt and had become historians. The Slitheen had not actually given up business, and were in conflict with a more influential family, the Blathereen. When the Doctor and Rose defeat an attempted Blathereen takeover of the system, the Slitheen are pleased to see they can once again become the profit-holders of their race. The Blathereen were mentioned again in the Sarah Jane adventures episode Revenge of the Slitheen.
In the Series 3 finale of The Sarah Jane Adventures, The Gift, a pair of Slitheen-Blathereen from an intermarried line of the two families attempted to overrun Earth with Rakweed, a plant native to Raxacoricofallapatorius and used as an addictive vegetable.
Rose mentioned the Slitheen Parliament of Raxacoricofallapatorius in "The Christmas Invasion" (though her impromptu speech was a pastiche of phrases she's picked up on her travels with the Doctor). A member of the Slitheen was captured by the Graske in the mini-episode "Attack of the Graske". Rose accused the Doctor (after his regeneration into the Tenth Doctor) of being a Slitheen in disguise in the 2005 Children in Need mini-episode and the Doctor makes a passing reference to the Slitheen and their skin-suits in "The Runaway Bride".
In the 2006 series episode "Love & Monsters", an alien called the Abzorbaloff, whose natural form is similar to that of the Slitheen, claims to be from Raxacoricofallapatorius' twin planet Clom. The Slitheen space ship from "Aliens of London" was also seen in a flashback in the same episode.
A Slitheen appears briefly in the Tenth Doctor novel The Nightmare of Black Island by Mike Tucker, created from Rose's memories, along with a Dalek and the Nestene Consciousness. The Slitheen are also briefly referenced by The Doctor in the same novel while speaking to a member of the Cynrog about hiding under human-like skinsuits. In the later novel, The Last Dodo, when the Doctor is asked if he's ever had a dream, he claims to have a recurring one in which a Slitheen on a rocking horse chases him.
The Slitheen appear in John Smith's A Journal of Impossible Things in the episode "Human Nature". The scribbled words by the drawing note that "it's always for money." A Fact File book about the Slitheen has also been released.
The Doctor Who website features a segment called Captain Jack's Monster Files, narrated by John Barrowman, which provides information about alien species. An episode focusing on the Slitheen  shows a family tree which makes reference to a number of other related families, all with the suffix, -een, with the exception of the "Absorbalovian Rebels", referring to the Absorbaloff from "Love & Monsters", from the twin planet of Clom.
Summary of appearances 
- Doctor Who
- The Sarah Jane Adventures
- Revenge of the Slitheen—September 24, 2007
- The Lost Boy—November 12–19, 2007
- "From Raxacoricofallapatorius with Love"—March 13, 2009
- The Gift—November 19–20, 2009
- The Nightmare Man-October 11, 2010
- "The Monsters Inside" (New Series Adventures) by Stephen Cole
- "The Slitheen Excursion" (New Series Adventures) by Simon Guerrier
- "Revenge of the Slitheen" (The Sarah Jane Adventures) by Rupert Laight
- "Attack of the Graske"—2005 (interactive episode)
One of the factors that helped the Doctor determine the home planet of the Slitheen was the fact that they had a hyphenated surname. Examples include the names Blon Fel-Fotch Passameer-Day Slitheen, and Jocrassa Fel-Fotch Passameer-Day Slitheen. Additional hyphenated forms in Slitheen names suggest family sub-units within the broader Slitheen family.
- Blon Fel Fotch Pasameer-Day Slitheen
- Sip Fel Fotch Pasameer-Day Slitheen
- Jocrassa Fel Fotch Pasameer-Day Slitheen
In the book The Monsters Inside:
- Dram Fel Fotch Happen-Bar Slitheen
- Ecktosca Fel Fotch Happen-Bar Slitheen
- Kist Mag Thek Lutivon-Day Slitheen
- Glune Fex Fize Sharlaveer-Slam Slitheen
- Korst Gogg Thek Lutivon-Day Slitheen
Individuals murdered by the family and used as skinsuits include:
- MP Joseph Green of Hartley Dale
- Margaret Blaine, a member of MI5
- Oliver Charles, transport liaison of the Prime Minister
- General Asquith, head of the British Army
- Assistant Commissioner Strickland of the London Metropolitan Police.
- Group Captain Tennant James of the Royal Air Force
- Ewan McAllister, Deputy Secretary of the Scottish Parliament
- Sylvia Dillane, chairman of the North Sea Boating Club.
- It is stated in "Invasion of the Bane" that K-9 Mark IV has been in a black hole for 18 months, "School Reunion" having taken place in 2007