Whose discovery led to the first vaccine against a deadly animal disease and later inspired vaccination?

Edward Jenner, an English physician, performed his famous experiment in 1796 after noticing that milkmaids who caught cowpox seemed protected from smallpox. He inoculated an eight-year-old boy, James Phipps, with cowpox material and later showed the boy was protected from smallpox. Jenner published his findings in 1798, and the practice spread rapidly. This breakthrough gave rise to vaccination, one of the most important advances in medicine. Smallpox was eventually eradicated worldwide in 1980.