William Clark, 1770–1838, American explorer, one of the leaders of the Lewis and Clark expedition, b. Caroline co., Va.; brother of George Rogers Clark. He was an army officer (1792–96), serving in a number of engagements with Native Americans. In 1803 he was chosen by his friend Meriwether Lewis to accompany the overland expedition to the Pacific. His observations of nature enlarged the findings of the expedition; his journals and maps recorded its history. In 1807, after the expedition had returned, Clark was appointed superintendent of Indian affairs, with headquarters at St. Louis, and from 1813 to 1821 he was governor of Missouri Territory. During the War of 1812, he led (1814) an expedition against the British and Native Americans in the upper Mississippi valley; upon reaching Prairie du Chien, Wis., he built Fort Shelby. Later, with Auguste Chouteau, he negotiated a number of important treaties with Native American tribes and aided in suppressing the Winnebago and Black Hawk uprisings. He was again superintendent of Indian affairs from 1821 until his death.
See bibliography under Lewis and Clark expedition.