Mason is a chimpanzee that resides in the Central Park Zoo with his fellow chimpanzee Phil. He has dark brown fur and serves as Phil's interpreter. He is the "Felix" of the Chimpanzees, being a fine and neat gentleman, which is opposite to Phil's attitude. Their difference doesn't entirely affect their friendship.

Mason is a very intelligent chimp who speaks with an English accent, though according to Private in Truth Ache, he is actually Canadian. He enjoys the finer things in life such as poetry, fine cuisine, and artwork, along with throwing poop at people. Unlike Phil, Mason is illiterate and can only read sign language. He is the darker color of the two chimps (in the series).