The Judoon are bipedal carbon based air breathing lifeforms whose body is rather humanoid and the head reminiscent of a Rhino. They are brutal but highly logical if not very intelligent. They have very developped lung capacity.
They have developed a spacefaring civilisation and serve as a mercenary police force in a section of the Milky Way in the beginning of the third millenium.
Source: Doctor Who "Smith and Jone" (TV) and "Revenge of the Judoon"