The smallpox vaccine is credited to English doctor Edward Jenner.
His reputation is well-earned, as he studied the disease and ways to prevent it for decades.
Jenner first used his vaccine by exposing an eight-year-old boy to a cowpox-infected needle. Although the boy suffered some symptoms from the cowpox, he was immune to smallpox.
But, a man tried this method years earlier despite spending his life trying to eradicate something far different: witches.
Cotton Mather was a popular minister and scholar in late 17th century Boston. The son of Increase Mather, another prominent minister, the duo were well-known advocates for the Salem witch trials.