Ja'far al-Sadiq

Born around 702, Ja'far ibn Muhammad became Imam at thirty-seven after his father's designation. Known as al-Sadiq - "The Truthful" - he founded the Ja'fari school of jurisprudence and taught Abu Hanifa and Malik ibn Anas, whose names anchor Sunni law. He stayed clear of the rebellions convulsing the caliphate, though Abbasid rulers harassed him and, Shia sources say, al-Mansur had him poisoned in 765. His death fractured the community: some followed his eldest son Isma'il, who'd died before him, spawning the Isma'ili branch; others accepted his younger son Musa al-Kazim, becoming the Twelvers. The theological doctrines of divinely designated succession, Imam infallibility, and protective dissimulation under threat all trace to him - or to those who spoke in his name.