Which god sacrificed himself to become the moon in the creation of the Fifth Sun?

Tecuciztecatl was the god who sacrificed himself and became the moon in the creation of the Fifth Sun.

In the Aztec creation story, the gods gathered at Teotihuacan to create a new sun after earlier worlds had been destroyed. Tecuciztecatl, a wealthy and boastful deity, volunteered for the dangerous transformation. Nanahuatzin, a humble and diseased god, also agreed to take part.

Tecuciztecatl hesitated when asked to leap into the sacred fire, but Nanahuatzin entered first and became the sun. Ashamed, Tecuciztecatl then threw himself into the flames and became a second heavenly body. The gods struck his face with a rabbit to dim his brilliance, explaining the moon's weaker light and the traditional association of lunar markings with a rabbit.

A common mix-up is Nanahuatzin: he sacrificed himself first and became the sun, while Tecuciztecatl followed and became the moon. The episode is part of the Mexica account of the Fifth Sun, the current cosmic age.