Answer:
You're talking about Richard Wagner
Explanation:
Wagner is responsible to introduce the concept of the musical theme (or leitmotif). His compositions tried to capture the essence and the History of German heritage, using nordic mythology as a starting point. The attempt to praise the heritage of his country lead him to compose operas that the strong and union of the German people, however, he constantly advocated avoiding the mixture with foreign populations, praising the German structure, and trying to maintain it pure, as he used to say. These ideas were crystallized by the Nazism years later. It was a genius with complexities.