Ma’at was both a concept and a goddess in ancient Egypt. Truth, order, balance, and morality, she stood on Ra’s boat that carried the sun through the sky. In the underworld she weighed your heart against an ostrich feather in a test for eternal life. If you failed, your heart was thrown into a lake of fire or devoured by a crocodile-cat-hippopotamus monster. Good times.
As a goddess Ma’at’s counterpart was Thoth, the mediator, but as a concept she also had a counterpart: Isfet. Isfet as a concept means chaos and injustice, but she too was also a goddess who had to be replaced by Ma’at before the world was born.
Duality seems to have great importance in every human mythology, from yin and yang to angels and demons. We like to simplify our desires and hates into opposing creatures, as if we can balance them on either side of a teeter-totter and watch them play.