The Undying mummies tell the tale of Khetamon, a wise ghul (as they call vampires) who turned from the path of darkness and cast himself before Osiris. According to legend, the god-king looked into Khetamon's heart and saw that he truly wished to cease feasting upon the living, but that he could not.
The First Pharaoh blessed the repentant Khetamon and taught him how to fight against the corruption that lurked within his spirit (implying that the discipline of Bardo was born out of this event). It is rumored that Osiris even let Khetamon drink his blood for purification, and upon seeing the god-king's mercy, other "blood demons" sought redemption for themselves. Since Osiris' strict religious discipline and deep philosophical teachings gave them new meaning, the repentant ghuls began to call themselves the Children of Osiris.