Lyon, Nathaniel (1818–1861), a United States army officer. His military actions early in the Civil War kept Missouri from entering the Confederacy. In May, 1861, Lyon was made a brigadier general and given command of Union troops at St. Louis. In June, 1861, he drove out the pro-Confederate Missouri governor and occupied Jefferson City, the capital. On August 10, 1861, Lyon's forces, outnumbered two to one, attacked Confederate troops and Missouri state militia at Wilson's Creek. Lyon was killed in the battle. He left his entire fortune, about $30,000, to the government for the war effort.

Lyon was born in Ashford, Connecticut. After graduation from West Point in 1841, he served in the Mexican War and on the western frontier.