The German composer Richard Wagner had an enormous influence not only on modern music but on artists of all stripes, and on political culture as well. His use of folkloric material to create modern epics won him the admiration of thinkers like W. E. B. Du Bois, and made him popular in Hollywood since the birth of film. Alex Ross, whose new book is called “Wagnerism,” tells David Remnick that Du Bois “might have seen ‘Black Panther’ as a kind of Wagnerian project.” And yet Wagner’s music was used to heroically represent the Ku Klux Klan in “The Birth of a Nation.” In fact, the composer’s strident anti-Semitism fed into the rise of Nazism in Germany. The many aspects of Wagner’s influence were often contradictory. “So much baggage arrives with him,” Ross says, but “we aren’t necessarily imprisoned by what the man himself thought.” The composer himself “starts to disappear” as his influence diffuses through society. “He becomes a mirror for what other people are thinking and feeling. And we have that right, we have that power with art. If there’s something about it we reject, we can—without forgetting or overlooking that darker aspect—remake it in our own image.”