Ecco the Dolphin

Ecco the Dolphin is the collective name given to a series of video games published by Sega which primarily take place underwater. They were originally developed for the Sega Mega Drive (known as the Sega Genesis in North America) and Sega Dreamcast video game consoles, but have since been ported to numerous systems. The games are named after their main character, Ecco, a young bottlenose dolphin. They are known for being unique and highly challenging titles. Ecco was created by E. Ettore "Ed" Annunziata, who also produced the Mega Drive game Chakan: The Forever Man.

The Ecco the Dolphin games hinge on the idea that cetaceans are sapient beings and have their own society under the waves. In the Mega Drive/Genesis games, humans are barely acknowledged and never by name. The cetaceans also call themselves "Singers". In the Dreamcast game, dolphins and presumably other cetaceans have united with humans in a cross-species society.