Mueller is of German, English and Scottish descent. His paternal great-grandfather, Gustave A. Mueller, was a prominent doctor in Pittsburgh, and his own father August C. E. Müller had immigrated to the United States in 1855 from the Province of Pomerania in the Kingdom of Prussia (a historical state whose territory included land now part of Germany and western Poland).[9] On his mother's side, he is a great-grandson of the railroad executive William Truesdale.[10]