His sister, Coyolxauhqui, killed their mother, Coatlicue, because she became pregnant in a shameful way (by a ball of feathers). Her fetus, Huitzilopchtli, sprang from her stomach and killed Coyolxauhqui, along with many of the brothers and sisters. He then tossed her head into the sky, becoming the moon, so that his mother would be comforted in seeing her daughter in the sky every night.
In art, he was represented as a hummingbird, or with just the feathers of such on his head and left leg, a black face and holding a snake and a mirror.