Robert Wilson’s avant-garde direction is enigmatic, to say the least, but this perceptive documentary reveals that his personal life was just as mysterious. Katharina Otto-Bernstein’s film carefully considers the creative process behind works like Einstein at the Beach and Black Rider, but it’s best mining his biography: His conservative childhood in rural Texas, his adoption of a disabled child and the strange, compelling way he worked him into stage pieces—not to mention all his years in New York. And it doesn’t hurt that the talking heads are people like Philip Glass and Susan Sontag.