The eighth of the Twelve Imams, son of Imam Musa al-Kazim and descendant of the Prophet. Appointed heir-apparent by the Abbasid Caliph al-Ma'mun, he died in 203/818 at Sanabad near Tus; the site of his grave grew into the great pilgrimage city of Mashhad. His shrine is among the holiest sites of the Shia world and is also venerated by Sunnis. (Sources: TDV 'Ali er-Rızâ'; Wikidata Q1144695.)