Born to a tanner in the Jura region, Louis Pasteur would go on to disprove spontaneous generation, invent pasteurization, and develop vaccines for rabies and anthrax. His insistence that invisible microbes caused disease overturned centuries of medical assumption and laid the foundation for modern microbiology and immunology.
Louis Pasteur grew up watching his father tan leather in a modest workshop, hardly the origin story one expects for a man who would rewrite the rules of biology and medicine. He was, by his own later admission, a mediocre student for much of his youth, more interested in fishing and sketching than in his lessons.
His eventual scientific rigor bordered on obsession. When he proved that fermentation and disease were caused by living microorganisms rather than spontaneous generation, he did so with swan-necked flasks so meticulously designed that skeptics could find no hole in his logic. Later, in 1885, he took an even bigger gamble: injecting a boy bitten by a rabid dog with an experimental vaccine he had never tested on a human. The boy, Joseph Meister, survived, and Pasteur became a national hero.
His name survives now mostly on milk cartons, a strange fate for someone whose actual legacy is the germ theory of disease, a concept so foundational to modern medicine that it's almost invisible in its ubiquity.