The "opening credits" sequence says "and Beavis as the Beavis", but in the actual "episode" portion, he is referred to as "Beaver" as well as "Beavis". This is because Eddie is making fun of him and nicknames him "Beaver".
Beavis/Beaver refers to one of his friends as 'Lumpy'. But in the original TV show, Lumpy was Wally's friend, not Beaver's - the writers perhaps got Lumpy Rutherford mixed up with Larry Mandello, who was a friend of Beaver.