His name was Sixto Rodriguez – the man the Associated Press called “the greatest protest singer-songwriter that most people never heard of.”

The death of the Detroit based musician was confirmed Wednesday by his granddaughter.

His albums flopped in the U.S. in the 1970s but, unknown to him, he became a star in South Africa where his songs about the Vietnam War, racial inequality, abuse of women and social mores inspired increased opposition to the country’s brutal racial system of apartheid.

The film tells the story of of two South Africans whose mission was to seek out their musical hero.  It won the Oscar for best documentary in 2013.

Sixto Rodriguez was 81.