The first presidential candidate of the Republican Party, John Charles Frémont was an explorer, politician, and soldier. Born on January 31, 1813, in Savannah, Georgia, Frémont was the son of John Charles Frémon and Anne Whiting Pryor. (The family added a "t" to its last name after Frémon's death.) Raised in Charleston, South Carolina, Frémont showed early talent in mathematics and the natural sciences. After attending Charleston College (1829-31), he taught mathematics on a ship and sailed to South America in 1833. In 1836, he helped survey a railroad route between Charleston and Cincinnati, Ohio, and in 1836-37 he worked on a survey of Cherokee lands in Georgia.

In 1838, Frémont obtained a commission as second lieutenant in the Corps of Topographical Engineers of the U.S. Army. Assigned to an expedition that...