Judoon
The Judoon were a race of rhinoceros-headed humanoids employed, as the Doctor put it, "police-for-hire" (or, he had added, appropriately, "interplanetary thugs"). (DW: Smith and Jones)
Biology
Judoon were two-metre high humanoids with a stocky build and rhinocerous-like heads. They had large lungs to help with breathing even in low-oxygen environments. (DW: Smith and Jones)
Behaviour
Judoon were brutish, with punishment that might seem cruel to some races (for example, physical assult gave the death penalty, "execution", one of the Judoon's favourite punishements) however they still operated under Galactic Law. They reserved the right to execute without proper trial, and if the suspect was not found, they could execute everybody in the location where they were searching, and they could probably destroy the entire area.
Their language was composed of many one-syllable words ending in a long "o" sound. Each sentance was composed of several of these words hyphenated together.
The Doctor described them them as logical but stupid and they seemed to favour methodical patterns of behavior, to a default. (DW: Smith and Jones)
Technology
"Execution" used a sort of gun to fire a disintegrating red energy beam.
The Judoon had scanners which tell the Judoon the species the scanned being, which spoke in a Judoon-like voice the name of the species. However, the scanners could be fooled by blood assimilated into the being's body, or by previous close contact with another species.
They also had trasnslation devices which worked by analysing the recorded voice of a being. The translators translated both ways.
They wear similar armour to the Sontarans but have no obvious affiliation to them. In general, their technology is a dark red or black colour, and most instruments, such as their weapons, scanners and translators, were thick and pen-shaped, simiar to a large sonic screwdriver. They did have a pen, a thick marker pen, used to mark "catalogued" people - those who had been scanned and deemed to not be a suspect - on their right hand.
The Judoon also have a contact device that reaches every Judoon helmet, allowing the Judoon Captain to give orders with a press of a button, albeit not pen-shaped.
Their spacecraft were gigantic, cylindrical craft, with four boosters at the bottom and four claws at the bottom which seved as landing gear. Each craft could hold several thousand Judoon in several hundred troops. The craft were pen-shaped, like most of the rest of their technology. The craft usually travelled in groups of three.
The Judoon could also use H2O Scoop to transport buildings across space and shield them with force fields is required by Galactic Law. (DW: Smith and Jones)
