Rilla Roo is a fictional character in the Crash series. He is a mutant hybrid between a gorilla and kangaroo, similar to how Dingodile is a crocodile and a dingo. His first (and only) appearance in a Crash Bandicoot game was in Crash Bash.
Note: The following is taken from the Crash Bash manual.
"Rilla Roo has the disposition of a train wreck. Though he prefers to take his time around the arena, his huge whipping tail delivers a nasty blow. Rilla Roo is a first stringer and considers himself a closer - and he doesn't like to have his photo taken. Watch out for this guy - he's not one to monkey around!"