A large, green, buck-toothed, and incredibly dim-witted fish from the Commander Keen game "Goodbye Galaxy!". It dwells in the Well of Wishes, on the planet Gnosticus IV, and is described as "the second-dumbest creature in the universe. Its thought patterns go 'swim swim hungry, swim swim hungry'". The Dopefish has become inexplicably popular, making cameo appearances in several other games from Apogee and Id, and even gaining a cult following on the web. Of course, such a popular fish has made several appearances in animutations.
Fun Fact: Calling it "the second-dumbest creature in the universe" is actually a reference to Douglas Adams' seminal Sci-Fi humour series The Hitchiker's Guide to the Galaxy, where the dumbest creature in the universe is the Ravenous Bug-Blatter Beast of Traal.