Who was the ruler of the Aztec empire when the Spanish conquest began?

The ruler of the Aztec Empire when the Spanish conquest began was Moctezuma II. He reigned from 1502 until his death in 1520, during which time the Spanish conquistador Hernán Cortés arrived in 1519. Moctezuma's initial interactions with the Spaniards were marked by intrigue, but ultimately led to conflict and the downfall of the Aztec Empire. His leadership faced significant challenges as the Spanish forces advanced and allied with various indigenous groups.