Joey is a kangaroo. He is an excellent fighter and doesn't like others tresspassing in his habitat.
His first appearance was in "assault and batteries". Skipper and King Julien had to escape from his habitat, while Joey was trying to beat them up all the time.
Joey was quite successful, but eventually Skipper and Julien managed to escape, by working together.
Although Joey is a strong fighter, he himself has been defeated several times. In "cat's cradle" the penguins lead officer X to Joey's habitat, because the hope Joey will beat up Officer X. But unfortunately Joey is no match for Officer X. In "Mort unbound" the strong muscled Mort also knew to beat Joey up easily.
Joey also made an appearance in "Skorca". He is there getting paid by the lemurs to take down the sky orca. However He is unsuccessful because his punches do not damage the giant balloon.