German recipients dominated the Nobel prizes in science. Germany dominated the world of physics before 1933, led by Hermann von Helmholtz, Wilhelm Conrad Röntgen, Albert Einstein, Otto Hahn, Max Planck and Werner Heisenberg. Chemistry likewise was dominated by German professors and researchers at the great chemical companies such as BASF and Bayer and persons like Justus von Liebig, Fritz Haber and Emil Fischer. Theoretical mathematicians Georg Cantor in the 19th century and David Hilbert in the 20th century. Karl Benz, the inventor of the automobile, and Rudolf Diesel were pivotal figures of engineering, and Wernher von Braun, rocket engineer. Ferdinand Cohn, Robert Koch and Rudolph Virchow were three key figures in microbiology.