Edward Jenner was an English physician and scientist born in 1749. He is best known for developing the first successful smallpox vaccine, which laid the foundation for immunology. Jenner observed that milkmaids who had contracted cowpox, a less severe disease, seemed to be immune to smallpox. In 1796, he tested this theory by inoculating a young boy with cowpox, demonstrating that it provided protection against smallpox. Jenner's work was groundbreaking and led to the eventual eradication of smallpox, a disease that had caused millions of deaths. His innovative approach to vaccination has influenced modern medicine and inspired the development of vaccines for various diseases, including polio, measles, and influenza.