Abū ʿAbd Allāh Muḥammad ibn ʿAbd Allāh al-Manṣūr, better known by his regnal name al-Mahdī, was the third Abbasid Caliph who reigned from 775 to his death in 785. He succeeded his father, al-Mansur.

Abū Jaʿfar ʿAbd Allāh ibn Muḥammad al-Manṣūr usually known simply as by his laqab al-Manṣūr (المنصور) was the second Abbasid caliph, reigning from 136 AH to 158 AH succeeding his brother al-Saffah. He is known for founding the 'Round City' of Madinat al-Salam, which was to become the core of imperial Baghdad.