This essay reviews the life and career of German scientist Ferdinand Cohn (1828-1898). A botanist by training, Cohn was a major force in establishing bacteriology/microbiology as a scientific discipline. He was a mentor of bacteriologist Robert Koch (Nobel Laureate 1905) and had significant interactions with Charles Darwin. Cohn was important in demolishing the erroneous idea of “spontaneous generation” of living organisms and was a pioneer in advancing concepts of microbial taxonomy.