Hernán Cortés de Monroy y Pizarro, 1st Marquis of the Valley of Oaxaca (; 1485 – December 2, 1547) was a Spanish Conquistador who led an expedition that caused the fall of the Aztec Empire and brought large portions of mainland Mexico under the rule of the King of Castile in the early 16th century. Cortés was part of the generation of Spanish colonizers who began the first phase of the Spanish colonization of the Americas.