RIchard Wagner
Perhaps one of the most polarizing figures in the field of opera, Richard Wagner is known for his prolific use of the leitmotif, a recurring theme through music, in his magnum opus, Der Ring des Niebelungen (The Ring of the Niebelung), a retelling of the German epic poem, Niebelungenlied. (English National Opera) Wagner was also known for his rather overt and extreme antisemitism and nationalism, long before the Nazi party would come to be. (Eylon) Much like Caspar David Friedrich, Richard Wagner was an artistic idol to Adolf Hitler, who was inspired after seeing Wagner's Rienzi to find his vision of creating his own version of Germany. (Music and the Holocaust) Wagner's views of Jewish people were so extreme that, since 1938, Wagner's music is banned from being performed in Israel (then Palestine at the time). (Bolton-Fasman)
Despite this, it cannot be denied that Wagner's impact on music is still felt today. Below, you can find a very brief synopsis of the Ring of the Niebelungen, which is a feat in and of itself to summarize so succinctly; the opera clocks in at about 15 hours, and can be even longer, depending on how fast the conductor of the opera wants to go! (Midgette)