William Walker was an American adventurer and filibuster in the mid-19th century, known for his attempts to expand U.S. territory in Central America. He led several expeditions, most notably to Nicaragua, where he briefly served as president in 1856. Walker aimed to establish English-speaking colonies and promote slavery in the region. His actions were controversial and faced opposition from both local populations and the U.S. government. After being ousted from power in Nicaragua, Walker made several more attempts to regain control but ultimately failed. He was captured and executed in Honduras in 1860, marking the end of his filibustering endeavors.