William Walker (May 8, 1824 – September 12, 1860) is an American lawyer, journalist and adventurer, who organizes several private military expeditions into Latin America, with the intention of establishing English-speaking colonies under his personal control, an enterprise known as "filibustering."

Walker becomes president of the Republic of Nicaragua in 1856 and rules until 1857, when he is defeated by a coalition of Central American armies, principally Costa Rica's army.

He is executed by the government of Honduras in 1860.