Question: Who is the featured in the documentary,  Imagine the Sound, and is known for his passionately Afrocentric music of the late 1960s?
Sentence (from "List of heavy metal festivals"): With roots in blues rock and psychedelic rock, the first heavy metal bands such as Led Zeppelin, Black Sabbath and Deep Purple attracted large audiences, and during the late 1960s and mid-1970s these band and others in their genre were featured at a number of historic rock festivals. Judas Priest helped spur the genre's evolution by discarding much of its blues influence.
Relevant evidence: No