Judoon were two-metre high humanoids with a stocky build and rhinoceros-like heads. They had large lungs to help with breathing even in environments with low levels of oxygen. Their thick skin was capable of withstanding most forms of attacks and their ears were capable of selective hearing. Judoon have yellow blood.
The Judoon were known for their strict obedience to the law and their brutal attempts in maintaining it. Crimes like physical assault of a Judoon incurred the death penalty, without chance for trial. The Doctor described them as logical, but stupid, and they seemed to favour methodical patterns of behaviour, to a fault. Even on crucial missions, Judoons would obey local traffic laws, 'Authorized personnel only' and 'Pay and Display' signs, follow mission procedure rigidly, and were required to get a form signed when commandeering transport.
Judoons slept with their boots on to show their dedication to their job. They also believed that a studded kilt was the sign of a warrior.
The Judoon were trained to use all known forms of transport, albeit not very well in the case of cars.
Their language was composed of many one-syllable words ending in a vowel, generally a long "o" sound but occasionally an "a". Each sentence was composed of several of these words hyphenated together.
Though they did not laugh, Judoons would shake and make a laughter-like noise when amused. Judoon do not like Opera.
In general, Judoon technology was a dark red or black colour, and most instruments, such as their weapons, scanners and translators, were thick and pen-shaped, similar to a large sonic screwdriver.
The Judoon had scanners which would tell the Judoon the species of the scanned being. However, the scanners could be fooled by previous close contact with another species. Metamorphic beings capable of altering their internal biology using assimilated biomatter could also deceive the scan. They also have pen, a thick marker pen, used to mark "catalogued" people - those who had been scanned and deemed not to be a suspect - on their right hand.
The Judoon also had translation devices which worked by analysing the recorded voice of a being. The translation was reciprocal. It also had a contact device that reached every Judoon helmet, allowing the Judoon Captain to give orders with a press of a button.
The Judoon Rockets were large cylindrical craft with four boosters, and four claws at the bottom which served as landing gear. Each craft could hold several thousand Judoon in troops of several hundred each. They were powered by ionic pulse fusion engines, allowing them to cross the solar system in 45 minutes. The ship were originally designed as military vessels and were shaped to strike fear in the hearts of their enemies. In the 25th century, the ships could also remotely teleport the Judoon.
The 'execution' punishment the Judoon were so fond of was delivered using a directed energy weapon with a red beam.
Judoon wore heavy black armour, which was sealed to allow them to survive in hostile environments. Their knees, feet, wrists and torsos were heavily armoured and reinforced for both offensive and defensive purposes.
- The Judoon could also use an H2O Scoop to transport buildings across space, and shield them with force fields as required by Galactic Law.
- In the 25th century, the Judoon were able to remotely lock down the communication and transport systems of spaceships.
The Judoon were originally a war-like race, until they became mercenaries for various Galactic organizations, including the Padrivole Regency and the Shadow Proclamation. They came to be one of the universe's most trusted mercenary races largely at the expense of the Ogrons, who had lost their dominant position as "hired guns" because of a string of defeats by the Doctor.
In the year 1902, while working for the Galactic Council, the Judoon were conned into assisting in a plot to use Temporal Reversion Devices on Earth. As they abducted Balmoral Castle during this, the misunderstanding would be known as the Balmoral Incident. As a result of this, the Judoon were banned from Earth.
At some point after the 1980s, the Judoon came to Earth, despite it being out of their jurisdiction. They came to the house on Allen Road, looking for an Eye of Akasha. The Doctor followed them and was forced to help them look for it. After they threatened Tegan, he handed it over and let them leave, but using slight of hand he switched the Eye with a Cricket ball.
The Judoon encountered the Sycorax at some point before 2006. The Sycorax who invaded Earth had belts made of Judoon skin.
In 2008, a Plasmavore who was pretending to be an old lady called Florence Finnegan murdered the Child Princess of Padrivole Regency 9 and then escaped to the Royal Hope Hospital. The Judoon used an H2O Scoop to transport the Royal Hope Hospital to the Moon, as they had no jurisdiction over Earth. The Plasmavore had drank the blood of a Human, though, and passed as a Human to their scanners. The Doctor was able to make her drink his blood, making her seem like an alien again. Martha Jones then convinced the Judoon to check her again and killed her when they found she was alien. The Judoon then returned the hospital to Earth. The Judoon were also investigating the Slitheen activities on Earth.
When the Doctor and Donna Noble came to the Shadow Proclamation to investigate the stolen planets, the Judoon were working as bodyguards for the Shadow Architect. In 2010, Captain Tybo of the 1005th Judoon Guard crashed on Earth while transporting the prisoner Androvax. Androvax escaped, and Tybo (wounded in his pursuit) was forced to accept help from Sarah Jane Smith and her friends. He was eventually able to track Androvax down and return him to custody. He initially sentenced Rani and Clyde to disintegration for interfering with his pursuit (by locking him in a EM shielded room), but he later commuted their sentence to planetary confinement after they helped prevent Androvax from escaping. In 2010 a Judoon was seen at the Zaggit Zagoo bar when the Doctor came to visit Jack Harkness one last time before his regeneration.
In 2487, the Judoon were investigating the Invisible Assassin and were able to track it to New Memphis. The Doctor believed they would cause more harm than good and agreed to work with the Judoon commander, Rok Ma, provided the other Judoon kept off the planet. With the help of Nikki Jupiter, they were able to find the Invisible Assassin, bring down two criminal empires and find the bombs planted within Terminal 13. After the mission, Rok Ma left the Judoon forces and joined Nikki's detective Agency.
Following the activities in the Silver Devastation, Judoon were sent to pick up the criminals.