The Rhino is a giant bluish-black cloud that is shaped like a rhino with yellow eyes.
Powers & Abilities
The Rhino is made of clouds so it probably can't be harmed. It seems to have the ability to control the weather because when it is seen, a strong wind comes and a storm cloud appears; and when it arrives, lightning appears afterwards followed by thunder. It also uses fear as a weapon; the more a person fears it, the stronger it gets. In fact, it represents James' fear.
In the book, the Rhino is a normal rhinoceros that escaped from the London Zoo.
In the movie, the Rhino was a mysterious monster, made entirely out of clouds, that resemble a rhinoceros. The Rhino came out of nowhere and gobbled up James' parents, forcing James to live with his two evil aunts, Spiker and Sponge.
Spiker and Sponge used the Rhino to scare James. It is unknown whether the Rhino was once a real rhinoceros when it killed James' parents, or if he is just a spirit haunting James (more likely the second one since rhinos are herbivores and don't eat meat).
When James and his best insect friends finally reached New York, the Rhino appears and tries to slow down their progress. Slowly, the Rhino approaches the giant peach, using the power of fear to frighten James. When James mustered up the courage to say he's not afraid of the Rhino, the Rhino ultimately dissolved, but not before shooting a final bolt of lightning at the giant peach.