Thomas Walker was a physician and explorer from Virginia; in the mid-18th century, he led an expedition to what is now the region beyond the Allegheny Mountains and the settled area of British North America. He was responsible for naming what is now known as the Cumberland Plateau and by extension the Cumberland River for the hero of the time, the Duke of Cumberland. His party were some of the first Englishmen to see this area; previous European explorers were largely of Spanish and French origins. Walker explored Kentucky in 1750, 19 years before the arrival of Daniel Boone.
Walker served as guardian for Thomas Jefferson, who was eleven years old when his second parent, his father Peter Jefferson, died in 1757. Two of Walker's own sons, John and Francis Walker, became US Congressmen.