Question: The 1909 "The Count of Luxemburg" was by a composer whose best known and most successful operetta was what?
Sentence (from "Karl Liebknecht"): Karl Liebknecht (] ; 13 August 1871 – 15 January 1919) was a German socialist and a co-founder with Rosa Luxemburg of the Spartacist League and the Communist Party of Germany.
Relevant evidence: No