Abu 'Abdallah Ahmad ibn Abi Du'ad al-Iyadi () (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 . 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 , 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. Early career Born in Basra in 776 or 777, Ibn Abi Du'ad belonged to an Arab family that originated from a village near Qinnasrin in northern Syria and which belonged to the Adnanite tribe of Iyad, although the latter claim was later contested by Ibn Abi Du'ad's enemies. Early in his life he moved to Damascus with his father, and he spent his youth learning Islamic jurisprudence (fiqh) and scholastic theology (kalam). His teacher Hayyaj ibn al-'Ala' al-Sulami had formerly been a pupil of Wasil ibn 'Ata', the founder of Mu'tazilism, and under his tutelage Ibn Abi Du'ad became an advocate of Mu'tazilite doctrines. Following the completion of his studies, Ibn Abi Du'ad became affiliated with Yahya ibn Aktham, the chief judge (qadi al-qudat) under the caliph al-Ma'mun (r. 813–833). It was while in Yahya's service that he first met al-Ma'mun – according to one anecdote, this occurred as early as the year of al-Ma'mun's arrival in Baghdad in 819 – and he quickly found favor with the caliph. Al-Ma'mun was himself inclined toward Mu'tazilism, which represented a moderate alternative between orthodoxy and the Alids while simultaneously affirming his authority as imam to preside over religious matters, and in