Edward Jenner (17 May 1749 – 26 January 1823) was an English physician and scientist, known for inventing the smallpox vaccine, the first vaccine in the world.
By the 18th century, smallpox inoculations were still dangerous and of limited efficiency. In 1796, Jenner discovered that being infected with cowpox, non-lethal to humans, gave immunity to smallpox. He made this discovery by infecting a young boy with cowpox, before trying to infect him with smallpox.
Due to his methods, Jenner's findings were frowned upon by the medical establishment. Thus, cowpox-based vaccination only saw wide use sometime after 1800.