The Blathereen Family are the antagonists of the Doctor Who book The Monsters Inside. They are a family from Raxacoricofallapatorius, the same planet the Slitheen Family come from who serve as business rivals to the Blathereen.
The Blathereen were originally a peaceful family who hunted down the Slitheen, but by 2501, they had become criminals. Like the Slitheen, the Blathereen disguised themselves by using the skins of humans, but unlike the Slitheen who used the bodies of obese people, the Blathereen had technology that could allow them use the bodies of both fat and thin people, though in The Sarah Jane Adventures, episode The Lost Boy, three Slitheen named Korst, Dax and Bloorm used the Blathereen's technology to use the bodies of thinner people too.
In 2501, a group of Blathereen led by Don Arco had taken over a star system prison named Justicia and planned to warp it into other solar systems and use it's sun into a flamethrower and destroy planets and use their remains as nuclear fuel (a plan similar to what the Passameer-Day branch of the Slitheen attempted to do with Earth). However, their plan was thwarted by The Ninth Doctor and some Slitheen who were imprisoned on Justicia.
In The Sarah Jane Adventures episode The Gift, it was revealed that some members of the Blathereen intermingled with members of the Slitheen, creation the Slitheen-Blathereen who looked down on the Blathereen, seeing them as weak and feeble and instead took after their Slitheen relatives. Two Slitheen-Blathereen named Leef and Tree Lorn Acre Slitheen-Blatereen attempted to turn Earth into a Rakweed farm, but were defeated by Sarah Jane and her friends.
- Arco Blathereen
- Ermenshrew Blathereen
- Clem Fel-Hetch Blathereen
- Unnamed Blathereen technician
- Blanc Blathereen