|First Appearance||The Hidden Valley of Oz|
Percy is a giant white laboratory rat.
He habitually calls himself "the personality kid," and talks like a street-smart American wise guy. (He calls everyone else "kiddo.")
Accompanying Jam on his travels and adventures, Percy grew to ten times his normal size by eating a magic muffin. He proved to be enterprising and resourceful. When Ozma sent Jam back home, Percy remained in Oz and got the Wizard to enchant him into his new large size permanently. (The Hidden Valley of Oz)
Rachel Cosgrove called Percy one of her favorite characters, and proved it by using him repeatedly in her Oz works. Percy has a major role in Cosgrove's other Oz-related book, The Wicked Witch of Oz, and returns again in her short story "Percy and the Shrinking Violet."