Richard Wagner

 was a German composer, whose works included the Liebestod from Tristan and Isolde and the Ring des Nibelungen. (TV: Silver Nemesis)

According to the Seventh Doctor, Adolf Hitler's favourite composer was not Wagner, but Franz Lehár. Klaus Fuchs was fond of Wagner's music. Ray Morita, on the other hand, thought it was "crap". (PROSE: Atom Bomb Blues) Oskar Steinmann loathed Wagner's work. (PROSE: Just War)

In a hallucination brought about by a morphine shot, a Wagnerian chorus heralded Captain Hartmann's discovery of the Holy Grail. (PROSE: Illegal Alien)

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

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.