George is an animal that the Gorilla jumped on top of at the end of the episode, "I Had an Accident." The zebra/horse is actually two people in the costume. "I Had an Accident" is his only appearance in the show. He is voiced by Dee Bradley Baker. He is a friend of the Gorilla.
"Let's get out of here!"
George is possibly a horse, not a zebra, because he has spots on him instead of stripes and the fact that horses are meant to be ridden on, rather than zebras.