Monster Files: Judoon

The Judoon are a race of mercenary police first appearing in the episode "Smith and Jones" (2007). They are basically humanoid in form, have heads that look like that of a rhinoceros, and wear black, bulky armour with heavy boots. As explained by David Tennant in a later interview, the name Judoon and the fact that the episode they appear in is set on the moon is an in-joke from the scriptwriter. As Tennant naturally has a Scottish accent one of the harder sounds to pronounce with an English accent is the 'oon' sound at the end of both words, including the line "a Judoon platoon upon the Moon".

Judoon are galactic police, brutal in their application of the law and highly logical in their battle tactics, but not very intelligent. They have no jurisdiction on Earth and no authority to deal with human crime, so when a fugitive alien hid out in an Earth hospital they transported the building to the moon. The Judoon carry energy weapons which can incinerate humans. In the hospital the Squad Leader is the only one seen to remove his helmet.