Hermann Muller

Several people are named Hermann Muller or Hermann Müller: 

Hermann Müller (1829–1883), German botanist who investigated coevolution between bees and flowers. Name has umlaut.
H.J. Muller (1890–1967), American geneticist who investigated mutations. Name has no umlaut.
Hermann Müller (SPD) Foreign Minister of Germany, 21 June 1919–26 March 1920. SPD party.