Who was Edward Jenner?

Edward Jenner (1749-1823) was an English doctor known primarily for his work in developing the smallpox vaccine. Smallpox was one of history's most deadly diseases. Highly virulent, it killed millions of people over the centuries before it was officially eradicated in 1980. Jenner's contribution was observing that those who had previously contracted cowpox, a related but significantly less dangerous virus, would not later contract the more lethal smallpox. Based on these observations, Jenner believed that inoculating people with the weaker cowpox strain would grant immunity against smallpox. He tested his assumptions in 1796, giving a child cowpox and later introducing smallpox into his system. As expected, previous exposure to the cowpox virus rendered the child immune. This discovery was a landmark moment in medical history and provided a means of combating one of history's most terrible diseases.
Jacquelyn G. Black, Microbiology: Principles and Explorations (8th edition), John Wiley & Sons: 2005, p. 586