Harvey is Emmet's friend in Emmet Otter's Jug-Band Christmas. He plays the kazoo and washboard in the Frogtown Jubilee Jug Band.
Although his full name isn't given in the TV special, he's called Harvey Beaver in the stage adaptation. In the original book, it's mentioned that Harvey is Hetty Muskrat's son. His appearance in both Henson versions suggests a change in species.