Abd Allah al-Radi

Abu ʿAlī al-Ḥusayn ibn Aḥmad ibn ʿAbd Allāh ibn Muḥammad ibn Ismāʿīl (Arabic: ابو علي الحسين بن أحمد ٱبْن عَبْد ٱللَّٰه ٱبْن مُحَمَّد ٱبْن إسْماعِيل, c. 825 – 881), also known as al-Zakī (lit. 'the pure'), al-Raḍī (lit. 'the satisfied one') and al-Muqtadā al-Hādī (lit. 'whose example should be followed, and guiding'), was a descendant of the Islamic prophet Muhammad and the tenth of the Isma'ili Imams, succeeding his father, Muhammad al-Taqi (d. 840). Before his death in 881, he entrusted the care of his son and successor, Abd Allah al-Mahdi who was then around 8 years old to his full brother, Sa'id al-Khayr, also known as Abu'l-Shalaghlagh.

With the death of Ja'far al-Sadiq in 148/765, Isma'il (d. 158/775) and Muhammad (d. 197/813), the gravity of persecutions of the Abbasids had considerably increased. The Isma'ili Imams were impelled to thicken their hiding, therefore, the first dawr al-satr came into force from 197/813 to 268/882, wherein the Imams were known as al-a'imma al-masturin (lit. 'the concealed Imams'). The concealment ended with the establishment of the Fatimid caliphate (r. 909–1171).