Walter "Wally" Monkey is Gus's 12-year old monkey partner and brother, and is considered the smarter of the two. He likes scaring people, eating bananas and playing video games. He is voiced by Mark Edwards.
Unlike Gus, Wally's fur is light and tan. He also wears a red rocket suit with a grey belt which has a star on it. He also has green and black eyes and spiky hair, along with a long tail and a pink nose. Unlike his big brother Gus, he has black eyes, which seem blue when enlarged, or in the Monkey Flashback when he was a baby. Wally also has buck teeth and is a little chunkier than Gus. He has a more raggedy tail and bushy eyebrows. Wally also has six toes on his right foot, as revealed in Tail Fail.
Wally is silly and optimistic, goofy, hyper, Darsage's (Darwin-kun) Friend. He likes to be very spontanious when it comes to missions and has more of a "kinder heart" when it comes to people, pets or missions than his older brother, Gus.
Wally has a good relationship with him because YAY-OK helps him with missions and he uses him as a video game player.
He has a crush on her that was shown in the episodes Love on Run and Monkey Hearts.