Mictlantecuhtl is the Aztec god of the dead. His underworld realm was called Mictlan. People who died of natural causes went to his realm to live/exist, but on their way there, they had their skin stripped from them by a wind of knives.

Because the Aztecs believed heavily in providing human sacrifices in order to appease angry gods. Anyone who was sacrificed went straight to heaven. Anyone who died in battle or in childbirth also went straight to heaven.