The Slitheen are a criminal family from the planet Raxicoracofallapatorius. They scavange planets looking for anything to sell for profit. They are big green aliens who disguise themselves in big humans. The Slitheen have one weakness they are made of calcium and they hate vinegar as if they get splashed with vinegar they blow up. The Slitheen fart a lot because of the gas exchange on Earth.The Slitheen infiltrated 10 Downing Street as Joseph Green who became PM, Margaret Blaine and Oliver Charles who's Slitheen later became General Asquith. They tried to blow up the world to sell it and make a lot of money. They made their spaceship crashe into Big Ben and then into the Thames. Doctors uncovered an alien body which turned out to be a pig. Its brain was wired up like nothing from Earth. When the Doctor went into Downing Street with lots of other important people they were all electricuted and killed except from the Doctor. He tried to tell everybody that the PM was an alien but nobody of course believed him. Meanwhile Rose Tyler, Harriet Jones and a secretary were being hunted by Margaret Slitheen. She killed the secretary and then Rose and Harriet. Lots more Slitheen were arriving disguised as government representatives. Meanwhile the Doctor saved Rose and Harriet from the Slitheen and locked all three of them in the cabinet room. Mickey and Jackie however were being hunted by a Slitheen police commander. However the Doctor figured out how to destroy them and so when Jackie got all of the vinegar she threw it onto the Slitheen and he blew up. The Doctor then made Mickey send a missile to Downing Street and when it was coming Downing Street was evacuated. When a guard went to tell the PM who wasn't in his disguise he ran in fear. The Slitheen tried to get into their skin suits but sadly were all blown up.
In Cardiff Margaret Slitheen was voted mayor of Cardiff. She wanted to destroy the Earth because the Doctor killed her family. She used a mechanical surfboard as he taxi away from Earth as if she returned home to Raxicoracofallpatroius she would be excecuted. The Doctor did take her out for an evening meal as a last request but Margaret several time did try to kill him but he out smarted her. When they arrived back at the Tardis Margaret used Rose as a hostage until she looked at the heart of the Tardis. Margaret was turned into an egg! The Doctor took her back home to start a new life once again.
Some Slitheen one Christmas were captured by the Graske who captured other aliens like Zygons and Scholars. We didn't see them that much but the Doctor let the Slitheen loose and they chased the Graske away for revenge.The Slitheen did fight Sarah Jane Smith later on as they wanted to avenge their families deaths thanks to the Doctor. They disguised themselves as school teachers. The school got a new block with a secret room full of alien technology. At each school built by coalgate corporation there was a smell of batteries and the food was always off. They were going to turn the sun cold and destroy the Earth for profit. The Slitheen needed some calculations and got them from Sarah Jane's son Luke Smith. Luke, Clyde and Maria were locked in the school and found out that some of the teachers were Slitheen and that a boy named Carl was a child of the Slitheen. However when Sarah Jane and her team raced to the school's secret room they were stopped by a Slitheen disguised as the headmaster. He was however blown up with vinegar by Maria Jackson. When the Slitheen heard about this they called for their other family members from stations in Washington, Paris, Santiago etc. Luke did tell them that the calculations he gave would destroy the Slitheen. After the machine was switched off Luke destroyed the room and killed Carl Slitheen's father. Some Slitheen escaped but didn't appear again.
The Slitheen fought Sarah Jane Smith once again but this time they were working with Mr Smith. They pretened that Luke was their son called Ashley so that he could generate enough power so that they could be rich. Unfortuantly Carl Slitheen returned as Nathan Goss and the Slitheen were double crossed by Mr Smith. The Moon was brought crashing down to Earth and Nathan tried to escape by failed. After the Slitheen helped Sarah Jane they left Earth in their spaceship.
Sarah Jane finally met the Slitheen once more but it would be for the last time. There were only two Slitheen but they tried to make Earth into a gigantic diamond. Unfortuantly they were foiled by another race from Raxicoracofallapatorius called the Blathereen who looked exactly the same but apart from they were orange.
Briefly in a bar in space where Captain Jack was at there was a Slitheen wondering about but only briefly.
The Slitheen have appeared in:
Series 1: Aliens of London, World War Three and Boom Town
2005 Christmas Special: Attack of the Graske
The Sarah Jane Adventures Series 1: Revenge of the Slitheen and The Lost Boy
The Sarah Jane Adventures Series 3: The Gift Part 1
Mentioned in Series 5: The Pandorica Opens
2010 Special: The End of Time Part 2