John C. Frémont
As an explorer, Army officer, and politician, John C. Frémont was a key figure in the nation’s westward growth. His expeditions charted previously little known territory for Congress and settlers migrating west. His father-in-law, the expansionist-minded Senator Thomas Hart Benton of Missouri, was instrumental in obtaining congressional funding for the expeditions and report that furnished Congress with facts for legislation on western territories. Frémont served as California’s first U.S. senator from 1850 to 1851. He ran unsuccessfully as the antislavery Republican Party’s first presidential candidate in 1856.