Walker, William (1824–1860), a United States filibuster, or military adventurer, who sought to build an empire in Central America. In 1853 he headed a small force that invaded Baja (Lower) California. He declared it an independent republic with himself as president, but soon was driven out. In 1855 he led an armed force that intervened in a civil war in Nicaragua on behalf of the revolutionary faction. He helped to establish a provisional government and eventually had himself named president. The United States recognized his regime in 1856. He was overthrown in a revolt backed by other Central American states in 1857. In 1860, while attempting to return to Nicaragua, he was captured and put to death by Honduran authorities.

Walker was born in Nashville, Tennessee.