Louis Pasteur

Pasteur proved the germ theory of disease—that microorganisms cause infection—overturning spontaneous generation and transforming medicine, surgery, and public health. He invented pasteurization in 1864, reducing pathogen counts in milk by 99.9%, and developed the first vaccines for cholera, anthrax, and rabies, saving the first human patient in 1885. His work is faster than the typical microbiological advance, laying the foundation for 80% of modern sterile practices in hospitals worldwide and directly influencing #9 James Clerk Maxwell's contemporary experimental methods.