William Clark in Louisiana Purchase and Lewis & Clark
William Clark (1770–1838), a lifelong military man, was asked by his friend Meriwether Lewis to serve as co-leader of the Corps of Discovery on its 1804 to 1806 round-trip journey across the continent of the Pacific.
Clark lacked formal education but nevertheless became the expedition's primary mapmaker and journal-keeper. Clark, a steady character, provided a perfect balance for Lewis' brilliant but more erratic—and possibly bipolar—personality.