Clark, William (1770–1838), a United States explorer. He was born in Caroline County, Virginia, and was a brother of George Rogers Clark. When William was 14, his family moved to the present site of Louisville, Kentucky. Clark saw military service in Indian wars, and became a skilled frontiersman. In 1803 he was chosen by his friend, Captain Meriwether Lewis, as co-leader of the expedition sent by President Jefferson to explore the great Northwest. Clark acted as mapmaker, artist, and astronomer for the expedition, and kept a valuable diary.

Clark later served as governor of Missouri Territory (1813–20), and as federal superintendent of Indian affairs. He laid out the site of Paducah, Kentucky, in 1828.