Rhino is a hamster and the tritagonist of Disney's 2008 animated film, Bolt.
He is Bolt's biggest fan. He has all but memorized every episode of the canine's TV show. So when Bolt shows up at his door, Rhino sallies forth in his hamster ball to help him out.
Though perhaps not the brightest of characters, Rhino does manage to help both Bolt and Mittens at times. Other than that, Rhino's function in the movie is more that of a "comic relief", offering little character development and personality, but quite a few humorous dialogues.
Rhino was also the central protagonist of his own short, Super Rhino, in which he got superpowers himself by Penny's father (just like Bolt). The short feature was added to the Blu-ray and DVD release.
Rhino's loud, lively and funny character made him an immediate favorite amongst certain movie-goers, but the character was met by mostly negative reviews from critics, often being described as a shallow, simplistic character that does little but steal attention from the more important characters like Bolt and Mittens.
Despite this, Disney had started an extensive advertising program using Rhino as their break-out character. The hamster was given a lot of focus in commercials, his own short-film was animated for the Blu-ray release and the studio even agreed to do some "fake", live interviews with a cut-in CGI animation of Rhino. These clips were spread on the internet prior to the DVD and Blu-ray release.
Rhino is the only character in the film that never realized that Bolt's superpowers aren't real, with Bolt seemingly seeing it unnecessary to tell the truth. However, in the ending, he watches the Bolt TV show and deems it "unrealistic," implying that he learned of the truth after being adopted by Penny.
It was implied in the movie that Bolt's relation to Rhino changed as the dog realized that he didn't have any superpowers. At first, Bolt was amazed with Rhino's lively, energetic character. But his simplistic, pedestrian view of himself and the world soon became a nuisance and after Bolt's quarrel with Mittens, he decides to continue without Rhino, leaving him behind in Las Vegas.
Rhino was listed #40 in Empire Magazine's The 50 Best Animated Movie Characters.
Rhino's voice actor Mark Walton was originally a placeholder voice, but the producers loved Walton's take on the character so much that he became the official voice.