The famous American explorer known for his expeditions in the Rocky Mountains is John C. Frémont.

Often called the "Pathfinder," Fremont led several significant expeditions in the western United States during the 19th century, including extensive exploration of the Rocky Mountains. His journeys helped map out the region and provided valuable information about the geography, resources, and native peoples of the Rockies. Fremont's explorations contributed to the westward expansion of the United States and influenced settlement patterns and the California Gold Rush.