Rhino is a hamster, originally owned by a little old lady, but has always been a TV fan. In particular he loved watching Bolt‘s show. He left home to help Bolt along his journey, still believing the dog to be a super hero. He is initially suspicious of Mittens because she is a cat (the villains of the show), though they eventually cooperate to help Bolt.
Rhino now lives with Bolt, Mittens, and Penny’s family.