Louis Pasteur was a chemist and microbiologist whose genius revolutionized medicine and food safety. He definitively disproved the theory of 'spontaneous generation' by showing that microbes come from other microbes in the air. This led to the 'Germ Theory of Disease,' which transformed hospital hygiene. Pasteur developed the process of 'pasteurization'—heating liquids like milk or wine to kill bacteria without spoiling the product. He also created the first vaccines for rabies and anthrax using weakened versions of the pathogens, a breakthrough that laid the foundation for modern immunology. His work saved countless lives and revolutionized industries ranging from agriculture to surgery.