Which Aztec emperor met Cortes in 1519?

Moctezuma II met Cortes on the southern causeway into Tenochtitlan on 8 November 1519 and brought him into the city as a guest. The city he was showing off was one of the largest in the world - somewhere around 200,000 people on an island in a lake, with aqueducts, causeways with removable bridges, and a market at Tlatelolco that the Spanish soldier Bernal Diaz said was bigger than anything in Rome or Constantinople.

He had been tracking the Spanish since they landed, sending embassies loaded with gold that were meant to impress and instead advertised exactly what was worth taking. Quite what he intended by letting them into the city is unrecoverable; the sources that claim to know his mind were all written by people with a reason to say he had lost it.

What actually happened is grubbier. Moctezuma was taken hostage in his own palace and kept as a mouthpiece. While Cortes was away dealing with a rival Spanish force, his deputy massacred celebrants at the festival of Toxcatl and the city rose against them. Moctezuma was dead within days, the Spanish were driven out over the causeways with heavy losses, and Tenochtitlan held for another year - by which point smallpox had done more damage than any fighting.