Answer
Hernán Cortés, a Spanish conquistador, played a pivotal role in the downfall of Moctezuma, the Aztec emperor. In 1519, Cortés landed in Mexico with a small force and formed alliances with native groups resentful of Aztec rule. Through a combination of military prowess, political maneuvering, and the devastating effects of European diseases, Cortés and his men eventually captured Moctezuma and conquered the Aztec Empire.