The invention of the first successful vaccine is credited to Edward Jenner, an English physician. In 1796, he discovered that milkmaids who had contracted cowpox did not catch smallpox. Jenner tested this theory by inoculating a young boy with cowpox and subsequently exposing him to smallpox, finding that the boy did not develop the disease. This groundbreaking work laid the foundation for immunology and the development of vaccines, ultimately leading to the eradication of smallpox and the creation of vaccines for various other diseases. Jenner’s work is recognized as a monumental step in public health and disease prevention.