Hummingbird of the South, (or Hummingbird of the Left) is the central deity of the Mexica. He is associated with the Sun and Fire. Huitzilopochtli is a warrior, armed the with the ferrocious Xiuhcoatl ("Fire Snake").
Huitzilopochtli is sometimes identified as the Blue Tezcatlipoca.
In the Huey Teocalli of Tenochtitlan (the major temple of ancient Mexico City) one half was dedicated to Huitzilopochtli, the other half to Tlaloc, the god of rain. Since war is called in atl in tlachinolli ("the water, the fire"), this combination of gods of fire and of water makes the major temple a place dedicated to the sacred war.
Huitzilopochtli has no direct relevance for the tonalpohualli. In the xiuhpohualli however, various festivals are dedicated to him.