Uncle Billy

 Uncle Billy  is the uncle of Oscar the Grouch. He is also the uncle of Ernest the Grouch  &  Otto the Grouch. Like Oscar 's father & Otto, Uncle Billy is never seen in any Sesame Street episodes. He is only mentioned in the 1976 book How to Be a Grouch, along with a few of Oscar's other relatives. Whether he is the brother of Oscar 's father  or  mother  is unknown.