Judoon
The Judoon are a race of rhinocerid humanoids employed as the galaxies mercenary police force, or hired guns. The Judoon were two-metre tall humanoids with rhinoceros-like heads and stocky build, with large lungs to assist their breathing when in environments with low levels of oxygen. Their ears are capable of selective hearing and their thick skins protect them from most forms of attack, though they had small brains, with one being able to fit in a chest that would be easily held in a humanoid palm. The Judoon race is known for their very strict obedience of the law and their brutal methods in maintaining it. Crimes such as physical assault of a Judoon would result in the death penalty without chance of a trail. The Doctor described them as stupid but logical, favouring methodical patterns of behaviour to a fault. To show their dedication to the job, the Judoon sleep with their boots on and also believe that a studded kilt is the sign of a warrior. Their language primarily composed of many one-syllable words evening in a vowel, with sentences comprising of many of these words strung together. The Judoon technology was similar to a large sonic screwdriver in that they were thick and pen-shaped, which was the shape used for their scanners, translators and weapons.
The Judoon scanners were capable of identifying a species, though the machine could be fooled by close contact with another species. The Doctor used this technique to distract the Judoon with Martha Jones by kissing her in Smith and Jones (Series 3 : Episode 1). They could also be fooled by assimilating the biology of another species, as used by the Plasmavore who drank the blood of humans and thus, appeared human to the Judoon scanner. The Judoon would mark "catalogued" people with a large black cross on their right hands. The Judoon translation devices worked by analysing the speech of someone. The translation itself was reciprocal, with the device having contact areas on it to connect it with a Judoon helmet, allowing the Captain to give orders with a press of a button. The Judoon had use of an H2O Scoop which they used to transport buildings across space and then shield them with force fields as they are required to do under Galactic Law. Their spaceships were large cylindrical craft with four boosters and four claws used as landing gear on the bottom. Each craft could house several thousand Judoon in troops of several hundred.
Before the Judoon became mercenaries for various Galactic organisations, including the Shadow Proclamation and the Padrivole Regency, they were a warlike race. At some point before 2006, the Judoon met, fought and lost to the Sycorax, who wore Judoon skinned belts as their victory winnings. In 2008, a Plasmavore escaped to the Royal Hope Hospital after murdering the Child Princess of Padrivole Regency 9. The Judoon used an H2O Scoop to take the hospital to the Moon as they had no jurisdiction on Earth to locate the Plasmavore. They succeeded with the help of the Doctor, who tricked the Plasmavore to drink his blood and making her appear alien on the Judoon's scanners. After finding her, they executed her. When the Tenth Doctor and companion, Donna Noble, went to the Shadow Proclamation following the disappearance of planet Earth, the Judoon were seen acting as security for the Shadow Architect.
The Judoon were seen in background capacities in 2010 at the Zaggit Zagoo bar when the Tenth Doctor met Captain Jack Harkness shortly before the Doctor's regeneration. They were also part of the alliance in 102A.D which caught and imprisoned the Eleventh Doctor in The Pandorica Opens (Series 5 : Episode 12). In the 52nd century, wheeler dealer Dorium procured the security software that the Headless Monks required by extracting it from the memory of a Judoon trooper. Later, a squad of Judoon were called upon by the Doctor when he invaded Demons Run to rescue his companion, Amy Pond, and her baby child, Melody, in A Good Man goes to War (Series 6 : Episode 7).