"Ride of the Valkyries" opens Act III of Wagner's opera
Die Walkure. The ride takes 8 minutes in the opera and has since taken a life of its own in pop culture. The most famous example is the helicopter attack in
Apocalypse Now.
Wagner himself is a controversial figure. He soaked up 19th century German anti-Semitism and glorified German nationalist themes. Some have tried to find anti-Semitism in his operas, but this is nothing more than people looking for something that is not there. Despite his nationalism and anti-Semitism, socialists tried to expropriate Wagner for their own uses. He was also Adolf Hitler's favorite composer and played a leading role in Nazi propaganda fifty years after his death. One of my college professors refused to listen to Wagner because of his anti-Semitism and posthumous ties to Nazi Germany.
The opening of Act III:
http://www.youtube.com/watch?v=1aKAH_t0aXA
Apocalypse Now:
http://www.youtube.com/watch?v=sx7XNb3Q9Ek