Ali al-Rida

Ali al-Rida (Ali ibn Musa, also called Abu al-Hasan and, in Persian, Imam Reza) is revered by Twelver Shia Muslims as the eighth of their twelve Imams — the line of leaders from the Prophet Muhammad's family whom Twelvers hold to be the rightful guides of the community. He was the son of the seventh Imam, Musa al-Kazim, and was born in Medina, the sources differ on the exact year, with reports clustering around 148-153 AH (roughly 765-770 CE).

His public significance came late in life. The Abbasid caliph al-Ma'mun summoned him from Medina to Khurasan, the northeastern province of the empire, and in 201 AH (817 CE), at the city of Marv (Merv), publicly named him heir-apparent (wali al-ahd, "successor to the caliphate"). Al-Ma'mun even changed the dynasty's official color from black to green and minted coins in al-Rida's name. Historians debate the caliph's motives — whether a sincere attempt to reconcile Sunni rule with Shia loyalties, or a political maneuver; the matter is not settled.

Al-Rida died in 203 AH (818 CE) at Sanabad near Tus while the court traveled west, and was buried beside the earlier grave of the caliph Harun al-Rashid. Shia tradition holds that al-Ma'mun had him poisoned; several Sunni historians record only a sudden illness. His shrine transformed the site into Mashhad ("place of martyrdom"), today one of the most visited pilgrimage cities in the Shia world.