Tragically, Wagner was the musician whose music changed the world most dramatically because he inspired Adolph Hitler and the National Socialists of Germany. Wagner was a great composer whose operas still resonate but who, unfortunately, held views that almost caused the destruction of the world and whose music embodied the myth of German racial superiority. To ignore this is to fail to face the truth. No other musician comes close. Without Wagner, there would have been no Holocaust.
He was the ultimate musical storyteller and revolutionized the role of the composer to include theatrical aspects that had been brushed off as unimportant. Not all of his influence was positive but it cannot be ignored. He was after all Hilter's favorite composer. I don't know if another musician can be linked to someone with so profound an effect on modernity.
Wagner's music, so romantic. heroic,sublime and stirring intoxicated Germans, bringing forth feelings of great nationalism, a raw emotion of power that allowed Adolf Hitler to capture and ride it as his white horse towards ethnic cleansing and a dream of world domination. His music - as beautiful as it was - became a powerful negative political force.
I do not think that he was the greatest composer of all time, but his influence in music, to this day, is still huge.You hear it almost every time you see a movie, watch TV, or even in commercials. He blew out the underpinnings of western music and they still have not been rebuilt. Whether this is good or bad--You figure it out. From Harry Potter to Star Wars and further his shadow falls. (How's that for purple prose?)
A favorite of Hitler, Wagner brought an over-the-top combination of anti-semitism and myth that probably had a strong influence on the NAZI/German disposition...