A mountain man is an explorer who lives in the wilderness and makes his living from hunting, fishing and trapping. Mountain men were most common in the North American Rocky Mountains from about 1810 through to the 1880s (with a peak population in the early 1840s). They were instrumental in opening up the various emigrant trails (widened into wagon roads) allowing Americans in the east to settle the new territories of the far west by organized wagon trains traveling over roads explored and in many cases, physically improved by the mountain men and the big fur companies, originally to serve the mule train-based inland fur trade.
Mountain men arose in a geographic and economic expansion that was driven by the lucrative earnings available in the North American fur trade, in the wake of the various 1806–1807 published accounts of the Lewis and Clark Expedition findings about the Rockies and the Oregon Country. They flourished for more than three decades, but their ability to make a good living through fur trapping had largely ended by the late 1840s—thanks to the rise of the silk trade, the collapse of the North American beaver-based fur trade since the 1830s, treaties signed in 1846 and 1848, and an upsurge in migration to officially settled western coastal territories in the United States.