Question: 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?
Sentence (from "Parsifal"): Parsifal (WWV 111) is an opera in three acts by German composer Richard Wagner.
Relevant evidence: No