The discoverer of vaccination is Edward Jenner, an English physician and scientist. He is credited with developing the world's first successful vaccine for smallpox in 1796. Jenner's work was based on the observation that milkmaids who had previously been infected with cowpox were immune to smallpox. He tested his hypothesis by inoculating a young boy with cowpox, and then later with smallpox, and found that the boy was immune to smallpox. This discovery revolutionized medicine and saved countless lives.