Otter, a recurring figure originating in Kenneth Grahame's literary work and appearing in various media adaptations including an anime series, shares a close friendship with Water Rat and frequently interacts with Mole and Badger. Lacking the significant wealth of some landowning acquaintances, his characterization takes inspiration from Cockney street vendors, evident in his distinctive speech patterns and overall demeanor.

He exudes confidence and a headstrong personality, often demonstrating protective instincts towards smaller companions like Rat and Mole, especially during perilous encounters within the Wild Wood. Otter functions as the primary source of riverbank gossip, leveraging his extensive social connections and deep familiarity with local happenings. He is father to a young son, Portly; the boy's temporary disappearance drives a key storyline where Rat and Mole search for him and encounter the mythological Pan.

Later canonical developments show Otter relocating away from the river due to threats from urban expansion, leaving his adult son behind. His eventual death occurs offscreen, with the name "Otter" passing to Portly. Otter's wife receives minimal mention across most adaptations, though supplemental materials suggest marital estrangement or divorce in certain versions. Within group dynamics, he participates in communal actions such as aiding in the reclamation of Toad Hall, though his contributions during celebrations sometimes face underappreciation by peers.

His visual design varies significantly across adaptations, sometimes depicted without clothing unlike fellow characters, while other illustrations feature period-appropriate swimwear. In select musical reinterpretations, both Otter and Portly undergo gender reassignment to female roles.