Geezer Butler is an English bassist. He formed and played bass for Black Sabbath, a pioneering heavy metal band, serving as their bassist and primary lyricist. Butler has released solo albums under the moniker GZR, including Black Science, Ohmwork, and Plastic Planet. He has also contributed to Ozzy Osbourne's solo projects. Butler has appeared in the documentaries Black Sabbath: The End of the End and Dio: Dreamers Never Die. He has also played with Deadland Ritual and Heaven & Hell.