John Coakley Lettsom FRS was an English physician and philanthropist born on Little Jost Van Dyke in the British Virgin Islands into an early Quaker settlement. The son of a West Indian planter and an Irish mother, he grew up to be an abolitionist. He founded the Medical Society of London in 1773, convinced that a combined membership of physicians, surgeons and apothecaries would prove productive. As the oldest such in the United Kingdom, it is housed in London's medical community at Lettsome House, Chandos Street, near Cavendish Square. Lettsom was its mainstay, as founder, president and benefactor.

The Medical Society of London is one of the oldest surviving medical societies in the United Kingdom.