The Beaver is the quinary antagonist in One Night at Flumpty's. Most often, he sits on the toilet, reading the newspaper and using toilet paper, and apparently does not like when he runs out of it. His exact origin is unknown, but Jonochrome said that he would try to come up with some story about the Beaver being a genetically modified hybrid of a beaver and a human.
He is absent in One Night at Flumpty's 2, due to falling in a toilet and dying, though note that Flumpty may have pushed him in.