Dennis is the deuteragonist of the 2001 children's animated series "Stanley". He is the pet goldfish and best friend of the main character, Stanley Griff. He lives in a round fish bowl, and although he likes exploring into the Great Big Book of Everything and teaching Stanley (and sometimes, fellow pets Harry and Elsie) about animals, what he doesn't like is when Harry and Elsie sing the book's theme song, which is why he doesn't like anyone mentioning the book. He even breaks the fourth wall by either asking the audience multiple-choice questions or encouraging them to do something themselves. Dennis is voiced by Charles Shaugnessy.

Dennis speaks to the kids in Stanley's class, as well as Stanley himself. The only adult that Dennis, Harry and Elsie ever speak to is Stanley's Grandma Griff.