Abu 'Abdallah Ahmad ibn Abi Du'ad al-Iyadi (Arabic: أبو عبد الله أحمد بن أبي دؤاد الإيادي, romanized: ʾAbū ʿAbd Allāh ʾAḥmad ibn ʾAbī Duʾād al-ʾIyādī) (776/7–June 854) was an Islamic religious judge (qadi) of the mid-ninth century. A proponent of Mu'tazilism, he was appointed as chief judge of the Abbasid Caliphate in 833, and became highly influential during the caliphates of al-Mu'tasim and al-Wathiq. During his tenure as chief judge he sought to maintain Mu'tazilism as the official ideology of the state, and he played a leading role in prosecuting the Inquisition (mihnah) to ensure compliance with Mu'tazilite doctrines among officials and scholars. In 848 Ibn Abi Du'ad suffered a stroke and transferred his position to his son Muhammad, but his family's influence declined during the caliphate of al-Mutawakkil, who gradually abandoned Mu'tazilism and put an end to the mihnah.
As one of the most senior officials during the reigns of several caliphs, Ibn Abi Du'ad's stature at the Abbasid court has been compared with that of the Barmakids at their height. Considered a leading Mu'tazilite and one of the chief architects of the mihnah, his persecution of orthodox scholars, including the famed theologian Ahmad ibn Hanbal, caused his reputation to suffer after his death, and he was made into an object of vilification by later Sunni biographers.
