The Doctor described Judoon as 'police-for hire', adding, 'They're more like interplanetary thugs'.
They have large lungs, powerful bodies and wear tough, black armour. The Judoon will punish physical assault with a judgement of death - implemented instantly and without compunction. They have a slavish obedience towards rules and when carrying out a law enforcement mission they're single-minded to the point of brutality.
No! Kro! Blo! Ko! Sho!The Judoon
The Judoon have worked for the Shadow Proclamation and during early encounters with the Doctor they indicated that he was not their enemy. Although they hunted him on the moon, their pursuit of the Time Lord boiled down to a case of mistaken identity. However, Judoon were amongst the alliance of the Doctor's old enemies who gathered at Stonehenge during events of The Pandorica Opens.