Dennis is the goldfish of Stanley Griff, and the deuteragonist of the 2001 Playhouse Disney (now Disney Junior) TV series Stanley. In fact, he is Stanley's best friend who gives him education about animals to help him with his everyday problems, which interest him. He also has to point out the flaws in Stanley's ridiculous solutions. He even breaks the fourth wall by either encouraging the audience to do something fun or by asking them questions at the end of almost every episode. He has musical talent and is sometimes shown to be playing the music for songs featured within installments of Stanley.
- Dennis has a cameo in an episode of Pinky Dinky Doo. He can be seen in a fish tank in the pet store. Porkchop, Stinky, Flick Duck, Harry, and Elsie appear as well. Just like Dennis, Harry and Elsie, the other three characters are from shows that the creator, Jim Jinkins, has created (Doug and PB&J Otter).
- He is sometimes considered the main character despite the show's title.
- It is revealed in the episode "A Boy's Best Friend is His Fish" that Dennis' breed of fish is a Comet.
- In one episode, Dennis says that rabbits are rodents, which is not exactly true.
- He has a similar personality to Cogsworth from Beauty and the Beast.
- He wears glasses to read.
- Dennis is the only one of Stanley's pets mentioned in the show's theme song, which asks "Who's proud to say his best friend is a fish?"