Richard Wagner

 was a German composer.

According to the Seventh Doctor, Adolf Hitler's favourite composer was not Wagner, but Franz Lehár. (PROSE: Atom Bomb Blues)

BOSS said that he and Stevens should have arranged for a symphony orchestra playing Wagner to herald his takeover of the world. (TV: The Green Death)

Klaus Fuchs was fond of Wagner's music. (PROSE: Atom Bomb Blues)

The Doctor thought that Ninani's attempt to pass herself off as a priestess of Ishtar was as convincing as an amateur vocalist working on Wagner's Ring without either a score or an ear for music. (PROSE: Timewyrm: Genesys)

Behind the scenes
Wagner's The Ride of the Valkyries was played at both the 2008 and 2010 Doctor Who Proms.