Slitheen

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Raxacoricofallapatorian
Doctor Who race
A child member of the Slitheen family as seen in Revenge of the Slitheen (2007)
First appearance	"Aliens of London" (2005)
In-universe information
Home world	Raxacoricofallapatorius
Type	Living calcium bipeds
Affiliation	Various (families)

The Slitheen are a fictional family of Raxacoricofallapatorians, massive, bipedal extraterrestrials, from the British science fiction television series Doctor Who. They are adversaries of the Ninth Doctor and later Sarah Jane Smith. The Slitheen are a family of egg-laying calcium-based aliens from the fictional planet Raxacoricofallapatorius. Though their family name is Slitheen, their species is named Raxacoricofallapatorians. The Slitheen are instinctive hunters, who are trained from a young age to be ruthless criminals whose main motivation is profit. They were convicted in their home world and are not willing to return to their planet in fear of receiving a death sentence.

The Slitheen 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 the spin-off series The Sarah Jane Adventures.