Abu al-Hasan al-Ash'ari

Abu al-Hasan Ali ibn Isma'il al-Ash'ari al-Basri al-Baghdadi was the founder of the Ash'ari school of Islamic theology (kalam). He studied under the Mu'tazilite theologian al-Jubbai for 40 years before famously debating and refuting him and publicly declaring his return to the way of Imam Ahmad ibn Hanbal and the Salaf. He then formulated theological responses to the Mu'tazilites and other deviant groups using the tools of kalam while affirming the beliefs of Ahl us-Sunnah. His works include al-Ibanah 'an Usul al-Diyanah, al-Luma', and Maqalat al-Islamiyyin. Note: Athari scholars hold that his final and correct position was expressed in al-Ibanah, which aligns with the way of the Salaf. He died in Baghdad around 324 AH.