David Thompson (1750-1857) was a trader, explorer and surveyor of what is now western Canada and the north-western United States, working for the Hudson Bay Company and then the Northwest Company. He travelled some 56,000 miles across North America, and mapped 1.9 million square miles. He was the first European to travel the full length of the Columbia River, and made the first contact of Europeans with a number of native American groups. He has been described as the “greatest practical land geographer that the world has produced”. He was noted for his accurate astronomical observations, using a sextant to determine latitude (from the altitude of sun and stars) and longitude (by the method of lunar distances). He married Charlotte Small, daughter of a Scottish father and a Cree mother. The couple had 13 children, lived in Montreal after Thompson’s retirement, and by the time of his death had been married 57 years, the longest marriage recorded in pre-confederation Canada. Find out more.