John Cunningham Lilly (January 6, 1915 – September 30, 2001) was an American physician, neuroscientist, psychoanalyst, psychonaut, philosopher, writer, and inventor. He was a member of a group of counterculture thinkers that included Timothy Leary, Ram Dass, and Werner Erhard, all frequent visitors to the Lilly home. He often stirred controversy, especially among mainstream scientists.

Lilly conducted high-altitude research during World War II and later trained as a psychoanalyst. He gained renown in the 1950s after developing the isolation tank. He saw the tanks, in which users are isolated from almost all external stimuli, as a means to explore the nature of human consciousness. He later combined that work with his efforts to communicate with dolphins. He began studying how bottlenose dolphins vocalize, establishing centers in the U.S. Virgin Islands, and later San Francisco, to study dolphins. A decade later, he began experimenting with psychedelics, including LSD, often while floating in isolation. His work inspired two Hollywood movies, The Day of the Dolphin (1973) and Altered States (1980), as well as the videogame series Ecco the Dolphin.