Claim: Hans Gregor led the Vienna State Opera where he was the first Vienna performances of Der Rosenkavalier, which is a German comic opera.
Evidence: From 1910 to 1918, he led the Vienna State Opera. There, he presided over such productions as the first Vienna performances of Der Rosenkavalier. Der Rosenkavalier (The Knight of the Rose or The Rose-Bearer), Op. 59, is a comic opera in three acts by Richard Strauss to an original German libretto by Hugo von Hofmannsthal.