What title was used for the ruler of an Aztec city-state?

The title used for the ruler of an Aztec city-state was tlatoani. In Nahuatl, tlatoani is derived from a verb meaning “to speak,” giving the title the sense of “one who speaks” or “one who commands.” Each altepetl, the Nahuatl term often translated as city-state, had its own tlatoani.

A tlatoani was more than a political ruler. The office combined royal authority with major religious, military, judicial, and economic responsibilities. The ruler oversaw tribute collection, temple affairs, market regulation, land, and the settlement of disputes. Although the position was usually dynastic and held for life, selection could involve a council choosing from eligible nobles.

The rulers of Tenochtitlan, Texcoco, and Tlacopan formed the governing alliance of the Aztec Empire. The ruler of the imperial alliance was more specifically called the hueyi tlatoani, meaning “great ruler.” This is why translating every tlatoani simply as “emperor” can be misleading: the title generally referred to the ruler of an individual polity, while the imperial ruler held a higher designation.