Ulayya bint al-Mahdi was an Abbasid princess born in 777 CE in Baghdad to Maknūna, a singer and concubine, and the third Abbasid Caliph, Muhammad al-Mahdi, who ruled from 775 to 785 CE. She was the half-sister of Harun al-Rashid, who ruled from 789 to 809 CE as the fifth caliph of the Abbasid dynasty, and who is portrayed as a central character in One Thousand and One Nights.