Monkeys (also known as Moo Goo or Monkius Nunchuckius) were minor enemy guards encountered in "Fire in the Sky" of Sly Cooper and the Thievius Raccoonus. They were employed by the Panda King to protect his stronghold in the Kunlun Mountains. Nothing can stop their training.
They were red monkeys with tan faces and stomachs. They wore white pants. As their weapon of choice, they used their nunchucks to attack their foes. Sly could defeat them with one single strike. They are enemies appearing only "The King of the Hill", "Flaming Temple of Flame" and "Rapid Fire Assault." While Murray does mention that monkeys are challenging him to a race in "A Desperate Race", it is never specified if the monkeys he was racing against are the same as these guards.
In "Flaming Temple of Flame," several monkeys can be seen training inside the temple. If Sly has found the blueprints for the Panda King's stronghold, Sly's binocucom will register them as breakable objects. Once "broken," however, if Sly looks at a monkey's former position, enemy data will still be displayed (provided Sly has obtained Bruce O'Coop's Computer Hacking ability beforehand).