Was the Abbasid Caliph Al-Ma'mun a Shiite?

The Abbasid Caliph Al-Ma'mun, Abdullah ibn Harun al-Rashid, was born in the year 170 AH and assumed the Caliphate in 198 AH, ruling for twenty years and five months. He was characterized by courage, justice, and strength in combat, and he personally adjudicated among the people.

Ibn Kathir mentioned that Al-Ma'mun had inclinations towards Shiism and Mu'tazilism, and was ignorant of the sound Sunnah. He pledged allegiance to Ali al-Rida as his successor and discarded the black banners, whereupon the Abbasids deposed him. However, he later triumphed over them, and the Caliphate was restored to him. Al-Ma'mun adhered to the Mu'tazili doctrine due to the influence of Bishr ibn Ghiyath al-Marisi. He loved knowledge but lacked insight, which led to the promotion of falsehood and its forced propagation in his later days.

Al-Ma'mun's Shiism was of the type that preferred Ali over the Companions, which the Salaf considered an affront to the Muhajireen and Ansar. Shaykh al-Islam Ibn Taymiyyah clarified that the Companions unanimously agreed on preferring Abu Bakr. Nevertheless, his Shiism was not of the extremist type like that of the Rafida; rather, it was a moderate Shiism that favored Ali without claiming divine designation (nass) or infallibility.

The innovation of Shiism was not the greatest in Al-Ma'mun's era; rather, the greatest innovation was the doctrine of the creation of the Qur'an, in addition to his consumption of intoxicants.