In his youth the future al-Aziz, then merely the third son of the caliph al-Muizz, acquired a concubine, most likely a Greek-speaking captive, and produced with her a daughter who was to become the famous Sitt al-Mulk. Not only did her mother remain al-Aziz’s favorite long after he rose to the Fatimid throne in 975, she remained so until her death twenty years later, and the daughter continued throughout to hold a claim on his attention many considered unusually intense and extraordinary. This favor, combined with her own political acumen and sharp intelligence, enabled Sitt al-Mulk to exercise authority throughout her lifetime until she finally became the real ruler of the empire upon the disappearance of her eccentric half-brother, al-Hākim, in 1021. Drawing on chronicles written by both Fatimid and anti-Fatimid historians, this article considers the context for Sitt al-Mulk’s rise to power amid the unusual dynamics of the Fatimid royal family. It reveals the implausibility of accounts that attempt to discredit her and demonstrates that when at last she governed the empire, she did so quite competently through a difficult time of transition.