Dennis is a an elderly fish that lives in Bikini Bottom. He first appears in the episode "Mermaid and Barnacle Boy."
He is a light green fish, light brown in "The Sponge Who Could Fly" and wears purple trunks with orange flowers on them. He also wears glasses and a tophat.
He is generally a background character in the show, and also appears as a member of the Mild Ones in "Born to Be Wild."