English explorer, trader, and geographer David Thompson (1770-1857) was born in London and educated at the Grey Coat School, Christ's Hospital School, and at Oxford University. While still in his teens, he came to Canada as an apprentice with the Hudson's Bay Company, but left in 1797 to become a partner in the North West Company. His extensive explorations of western Canada included the discovery of the source of the Columbia River in 1807, and he surveyed the entire river in 1811. He established trading posts throughout the Pacific Northwest, including ones on the Kootenai, Pend Oreille, and Spokane rivers. In his later years, he created a comprehensive map of the northern United States and Canada, based on the surveys he and others had completed. From 1816 to 1826, he headed the British commission that established the boundary between the U.S. and Canada. His old age was marred by poverty, and his work was largely forgotten until the posthumous publication of his writings in the early 1900s.