Which Aztec emperor (tlatoani) was ruling when the Spanish arrived in 1519?

Moctezuma II was the Aztec emperor ruling when the Spanish arrived in 1519.

Also known as Motecuhzoma Xocoyotzin or Montezuma, Moctezuma II was the ninth huey tlatoani of Mexico-Tenochtitlan. He came to power around 1502 or 1503, succeeding Ahuitzotl, and ruled during the empire’s greatest territorial extent.

When Hernán Cortés landed on the Gulf Coast in 1519, messengers quickly informed Moctezuma. Cortés reached Tenochtitlan on 8 November 1519, and Moctezuma met the Spanish-led force at the city’s entrance. The encounter began with diplomacy but soon turned into a political crisis: Cortés took the ruler captive, using him to pressure the Mexica government.

Moctezuma’s death in 1520 remains disputed in its precise circumstances. Spanish accounts say he was killed while addressing his subjects; Indigenous accounts and later interpretations describe possible Spanish involvement. He was followed briefly by Cuitláhuac and then by Cuauhtémoc, the final Mexica ruler during the siege and fall of Tenochtitlan.