The Beast was a huge serpent that Sly Cooper encountered in Mz. Ruby's swamp in Haiti. During the job "The Lair of the Beast," Sly explored the Beast's territory in search of a treasure key but ended up running for his life when the Beast awoke. Because of its tremendous size, the Beast could not be damaged. However, Sly later used the Beast to bash through a barricade to gain access to the other section of Mz. Ruby's production facility.
The Beast is a large and flexible creature with red and yellow scales, as well as red-pink eyes, razor sharp teeth and a snake-like tongue. Sly's cane would have little to no impact on it. It also breathes a green, toxic-like fume when it roars.
Due to its fearsome and vicious nature, nearly every character feared it, including Mz. Ruby, who kept it in a large swamp area with one of her treasure keys.