Huitzilopochtli (or “hummingbird”) was the chief god of the Aztecs and was called their god of war. According to legend, it was Huitzilopochtli that urged them to leave their original homeland and led them to the Mexico Valley region. It is believed that when they left the area of what is now the southwestern U.S., they nomadicallymigrated south and reached the region where they built the city of Tenochtitlan.
The legend of Huitzilopochtli tells the story of his mother being shamefully impregnated with him by a ball of feathers. This is why his siblings were determined to kill their pregnant mother; instead, the story says Huitzilopochtli was born full-grown and came out fighting. He was born to battle and became revered as the national god of the Aztecs. He was a god of war, the sun god, the god of death, and a fearsome guide for all journeys of the Mexica.
Text taken from http://www.allabouthistory.org/huitzilopochtli-faq.htm