Osiris' Sis is a reference to the Egyptian goddess Isis. Isis was the wife of Osiris, the god of the afterlife, and was known as the goddess of motherhood, magic, and fertility. She was also the protector of the dead and the goddess of children. She was often depicted with wings and a headdress of cow horns and a sun disk. Isis was one of the most important gods in ancient Egypt and was worshipped throughout the country.