Maat was the Egyptian Goddess of truth, justice and harmony. A daughter of the sun God, Ra, she ruled over the judgement of the dead in the throne room of Osiris. Each person, when they died, had to appear before the 42 judges of the dead and declare whether they were innocent or guilty of numerous crimes. The soul of the dead person would be weighed on a pair of scales against the Goddess, represented by a single ostrich feather.
The scales were held by the God Anubis, and their verdict was recorded by Maat's consort, the moon god Thoth. If the heart was weighed down by crimes, the terrifying female monster Ammut, part crocodile, part hippopotamus, part lion, would devour the dead person. However, if the deceased had lived "with Maat in his heart", and was thus pure and virtuous, they became a spirit, and could live with the Gods to fight against the serpent Apep.