This is Roger Rhino, an obscure character in an obscure Richard Scarry book. Julia has been obsessed with Roger Rhino for weeks now, regularly spending hours a day "being" Roger Rhino - which entails little more than repeating "I'm Roger Rhino!" with a big smile on her face and occasionally giving me a gentle butt with the "big horn" on the bridge of her nose.
Honestly, I can't figure out why on earth my sweet little blonde girl likes to pretend to be a gray-skinned, hardhat-wearing pachyderm with anger management issues and the ability to accidentally crush stupid Pa Pig's cars. Or maybe that is the explanation...
(Free bonus fact from Wikipedia: "the collective noun for a group of rhinoceros is 'crash'.")