Fur Trader, Explorer, Surveyor, and Cartographer (mapmaker).
Born in England, Thompson was a boy of fourteen when he joined the Hudson's Bay Company fur trade and sailed to York Factory on Hudson Bay in 1784. Almost from the start of his career, Thompson showed more interest in exploration than in trading for furs.
He left the Hudson's Bay Company in 1797 to join its rival, the North West Company (NWC), because it was willing to grant him more time to make a map of their fur trade posts and the rivers and lakes that connected them. Thompson's mapping covered more than 2.5 million square kilometres of North America during his lifetime. This is the greatest achievement in land geography of all time!
Thompson mapped most of the West. He travelled south to the Missouri River in the United States, and he mapped the sources of the Mississippi River, as well as the shores of the Great Lakes. Then, in 1806, Thompson began searching for mountain passes that would take him from the Prairies into the Pacific Slope (the part of Canada now known as the province of British Columbia, and the part of the USA now known as Idaho and Washington states).
His greatest achievement on the Pacific Slope was his mapping of the Columbia River. He canoed both down and up it with voyageurs in 1811. Thompson's Métis wife, Charlotte Small, and their children almost always travelled with him on his long and arduous trips. They are a famous early Canadian family.
Thompson and his family retired from the fur trade and left the West in 1812. He built a house in Williamstown ON and continued his interests in surveying and mapmaking. That house is a museum today. Thompson did not complete a book during his lifetime, but portions of his journals have been published three times.