Jaʿfar ibn Muhammad al-Muʿtasim bi'llah (; March 822 – 11 December 861), better known by his regnal name al-Mutawakkil ʿala Allah (, "He who relies on God") was an Abbasid caliph who reigned in Samarra from 847 until 861. He succeeded his brother al-Wathiq and is known for putting an end to the Mihna "ordeal", the Inquisition-like attempt by his predecessors to impose a single Mu'tazili version of Islam.