Gertrude is a fantasy creature that features in Sue Ellen’s fantasy in the episode “The Secret Guardians”. She is a pet cannawannabe, a creature from the jungles of Borneo which only eats walnut shells. She looks like a crocodile with a crest like a triceratops.
When Sue Ellen wants to join the Explorer’s Club for discovering the lost civilization of Arsubia, but does not have enough evidence, Gertrude's master orders Gertrude to push Sue Ellen out of the club.