The SlitheenThe Slitheen were first seen in Aliens of London (Series 1 : Episode 4) and World War Three (Series 1 : Episode 5) as a large criminal family from the planet Raxacoricofallapatorius. The Slitheen are creatures of living calcium, who were once rulers of their planet, but in their rule their economy crashed and the population rose up against them. The Slitheen family were sentenced to death but many escaped. In March 2006, many Slitheen had disguised themselves using compression technology to fit into the skin suits of dead humans. A side effect of the compression did mean that the Slitheen would expel a lot of gas, similar to human flatulence.
During their invasion in March 2006, the Slitheen family had taken over most of the British Government members by killing them and wearing their skin. The Slitheen intended to start a nuclear war against fictitious aliens and turn Earth into a nuclear reactor pile and sell the remains off as starship fuel. During this attempt, the Slitheen notably posed as:
- Margaret Blaine – Head of MI5
- Joseph Green – Politician and then Prime Minister of Great Britain
- PC Strickland – Police Officer
Later, in September 2006 in the episode Boom Town (Series 1 : Episode 11), Blon (still posing as Margaret Blaine and only surviving Slitheen from the Ten Downing Street explosion), managed to get herself elected as Mayor of Cardiff. In this position she tried to blow up Earth by destroying a local nuclear reactor and use the Cardiff Time-Space Rift to amplify the explosion which would destroy Earth and allow her to escape. The Doctor foiled this plan when Blon tried to use the TARDIS to help her escape. Blon ended up reverting back into an egg form of a Slitheen, where the Doctor took her back to Raxacoricofallapatorius where she was given a second chance at life.
Members of the Slitheen family were also part of the alliance at the end of Series 5 to imprison the Eleventh Doctor inside the Pandorica.