He was known for playing in back gardens performing 18th- and 19th-century-style ballads on weekends, while sustaining himself financially working as a forklift driver at a car plant.
[2] Schleinstein was featured in a documentary, Bruno der Schwarze – Es blies ein Jäger wohl in sein Horn (1970).
[3] When Werner Herzog saw the film, he promptly cast Schleinstein (under the name Bruno S.) as his lead actor in The Enigma of Kaspar Hauser (1974), though he had no acting experience, and the historical figure he portrayed was only in his teens.
Bruno, with his strength and vulnerability, with his head tilted back and his eyes opened wide as if to receive every signal coming in, with his gift for the unexpected gesture, not only inhabits the role but seems to have fathered it.
Herzog has claimed that Schleinstein 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.
Schleinstein appeared in Jan Ralske's short documentary film Vergangen, vergessen, vorüber (lit.