Nemo the Clownfish is the eponymous protagonist of the 2003 Pixar's animated film Finding Nemo; he is also a major character in the 2016 sequel Finding Dory.
The only son of Marlin, Nemo is a young clownfish inhabiting the Great Barrier Reef off the coast of Australia. Due to his father's overprotectiveness, Nemo was challenged by his father's lecturing of the world beyond the Reef, eventually leading him to become separated from him after a group of human divers kindapped him for sport.
Though not physically seen in Disney Heroes vs. Villains at present, Nemo is mentioned as the primary objective of his father's goal to reunite with him in the future.