Sir John Smith of Grothill was the Provost of Edinburgh in 1645.
He was infected with the bubonic plague, and also had a Grief Leech attached to his stomach. The leech was removed by the Twelfth Doctor who then cured Smith with a tablet from the TARDIS.
He later led the people of Edinburgh in defeating the Grief Leeches with the help of the Doctor and his companions. (PROSE: Plague City)