Huitzilopochtli (Classical Nahuatl: Huītzilōpōchtli, IPA: [wiːt͡siloːˈpoːt͡ʃt͡ɬi] ^ⓘ) is the solar and war deity of sacrifice in Aztec religion. He was also the patron god of the Aztecs and their capital city, Tenochtitlan. He wielded Xiuhcoatl, the fire serpent, as a weapon, thus also associating Huitzilopochtli with fire.

The Spaniards recorded the deity's name as Huichilobos. During their discovery and conquest of the Aztec Empire, they wrote that human sacrifice was common in worship ceremonies. These took place frequently throughout the region. When performed, typically multiple victims were sacrificed per day at any one of the numerous temples.

There continues to be disagreement about the full significance of Huītzilōpōchtli's name. Generally it is agreed that there are two elements, huītzilin "hummingbird" and ōpōchtli "left hand side." The name is often translated as "Left-Handed Hummingbird" or "Hummingbird of the South" on the basis that Aztec cosmology associated the south with the left hand side of the body.

However, Frances Karttunen points out that in Classical Nahuatl compounds are usually head final, implying that a more accurate translation may be "the left (or south) side of the hummingbird".

The hummingbird was spiritually important in Aztec culture. Diego Durán describes what appears to be the hummingbird hibernating in a tree, somewhat like the common poorwill does. He writes, "It appears to be dead, but at the advent of spring, ... the little bird is reborn."

There are a handful of origin mythologies describing the deity's beginnings. One story tells of the cosmic creation and Huitzilopochtli's role in it. According to this legend, he was the smallest son of four — his parents being the creator couple of the Ōmeteōtl (Tōnacātēcuhtli and Tōnacācihuātl) while his brothers were Quetzalcōātl ("Precious Serpent" or "Quetzal-Feathered Serpent"), Xīpe Tōtec ("Our Lord Flayed"), and Tezcatlipōca ("Smoking Mirror"). His mother and father instructed him and Quetzalcoatl to bring order to the world. Together, Huitzilopochtli and Quetzalcoatl created fire, the first male and female humans, the Earth, and the Sun.

Another origin story tells of a fierce goddess, Coatlicue, being impregnated as she was sweeping by a ball of feathers on Mount Coatepec ("Serpent Hill"; near Tula, Hidalgo). Her other children, who were already fully grown, were the four hundred male Centzonuitznaua and the female deity Coyolxauhqui. These children, angered by the manner by which their mother became impregnated, conspired to kill her. Huitzilopochtli burst forth from his mother's womb in full armor and fully grown, or in other versions of the story, burst forth from the womb and immediately put on his gear. He attacked his older brothers and sister, defending his mother by beheading his sister and casting her body from the mountain top. He also chased after his brothers, who fled from him and became scattered all over the sky. This same story exists also with Quetzalcoatl instead.

Huitzilopochtli is seen as the sun in mythology, while his many male siblings are perceived as the stars and his sister as the moon. In the Aztec worldview, this is the reason why the Sun is constantly chasing the Moon and stars. It is also why it was so important to provide tribute for Huitzilopochtli as sustenance for the Sun. If Huitzilopochtli did not have enough strength to battle his siblings, they would destroy their mother and thus the world.