Aquadog used to belong to Janet Reed and was amongst the people encased by the Trench in their feeding cocoons, and was found inside alive by Aquaman, allowing him to figure out that the rest were alive and able to be saved. After Aquaman and Mera finish dealing with the Trench, they're visited by the deputy who first contacted them about the threat, and are given the dog who is now with out an owner. As a joke, the deputy suggest they call the dog "Aquadog" and informs them that he doesn't know how to swim. His exact breed is unknown but he resembles a Golden Retriever.
Aquadog was created by Aquaman writer Geoff Johns.
Major Story Arcs
For more information see: Aquaman: The Trench
For more information see: Aquaman: The Others
Aquadog is seen waiting at the light house when Aquaman and Mera return after fighting Black Manta.