Bruno was the unwanted son of a prostitute and was often beaten as a child. As a result, he spent much of his life in mental institutions. Bruno was spotted by director Werner Herzog in the documentary Bruno der Schwarze - Es blies ein Jäger wohl in sein Horn (1970). Herzog promptly cast Bruno, a street musician with no experience of acting, as his lead actor in The Enigma of Kaspar Hauser (1974).
He is a largely self-taught musician, who, over the years developed considerable skill on the piano, accordion and glockenspiel. He would play in "back yards" performing 18th and 19th century style ballads on the weekends, while sustaining himself financially working as a forklift driver at an automotive plant. His music has earned him genuine respect in his community.
Bruno also starred in Stroszek (1977), which Herzog wrote in a few days especially for him, apparently to compensate for having cast Klaus Kinski in Woyzeck at the last minute instead of Bruno. Stroszek has a number of biographical details from Bruno's life, including the use of his own flat as the home of Bruno Stroszek. He also plays his own instruments. Herzog has claimed that Bruno was deeply suspicious of the director, and nervous of performing in front of the cameras so had to be "listened to" for several hours on set in order to build his self-esteem.
Bruno S. remains somewhat enigmatic and has not acted since. Instead, he took up painting and music. Some of his artwork was shown at the 2004 Outsider Art Fair in New York City.