Cousin Fungus is a relative of The Addams Family.
When Gomez and Morticia first met, she heard him cackling and followed the sound to the secret tunnel off the Play Room. Gomez said Fungus "doesn't get out much. He has lived in a cave in back of the tunnel for thirty years." Morticia eyes the tunnel and says he has exquisite taste.
The Addams Family original series episode: