In Aztec mythology, the guardian of the underworld is Mictlantecuhtli, the god of death and the ruler of Mictlan, the underworld. He is often depicted as a skeletal figure adorned with various symbols associated with death. Mictlantecuhtli guided the souls of the deceased, determining their fate in the afterlife. His presence emphasizes the significance of death and the afterlife in Aztec culture and reflects their beliefs regarding the duality of life and death.