What 9th-century German composer conceived and promoted the idea of a special festival to showcase his own works, in particular his monumental cycle that is an opera in three acts that is loosely based on "Parzival" by Wolfram von Eschenbach?
Bayreuth Festival: The Bayreuth Festival (German: Bayreuther Festspiele ) is a music festival held annually in Bayreuth, Germany, at which performances of operas by the 19th-century German composer Richard Wagner are presented. Parsifal:  It is loosely based on "Parzival" by Wolfram von Eschenbach, a 13th-century epic poem of the Arthurian knight Parzival (Percival) and his quest for the Holy Grail (12th century).
Richard Wagner