Abu Mansur Buya (Persian: ابو منصور بویه‎‎; died 983), better known his honorific title of Mu'ayyad al-Dawla (Persian: مویدالدوله‎‎; "Helper of the Empire") was the Buyid amir of Hamadan (976–983), Jibal (977–983), Tabaristan (980–983), and Gorgan (981–983). He was the third son of Rukn al-Dawla.

Abu Mansur Buya was the son of Rukn al-Dawla and a daughter of the Dailamite Firuzanid nobleman Al-Hasan ibn al-Fairuzan, who was the cousin of the famous military leader Makan ibn Kaki. Abu Mansur Buya lived in Isfahan during his youth. In 955, a Dailamite military officer named Muhammad ibn Makan, attacked Isfahan. Abu Mansur Buya, along with family and followers, were then forced to leave the city.

The eldest son of Rukn al-Dawla, 'Adud al-Dawla, along with Rukn al-Dawla's vizier Abu 'l-Fadl ibn al-'Amid, then marched towards Isfahan and defeated Muhammad ibn Makan. After Isfahan was under safe Buyid hands once again, Abu Mansur Buya along with his family and followers then returned to the city. In ca. 958, Abu Mansur Buya went to Baghdad, and married Mu'izz al-Dawla's daughter Zubayda. After the marriage, he along with her returned to Isfahan. Later in 966, Abu Mansur Buya was given the honorific title of "Mu'ayyad al-Dawla"

As part of the settlement between Rukn al-Dawla and his eldest son 'Adud al-Dawla in early 976, Mu'ayyad al-Dawla was to receive Hamadan upon his father's death, in exchange for recognizing 'Adud al-Dawla as senior amir. Only a year later, Rukn al-Dawla's second son Fakhr al-Dawla, who ruled in Ray, rebelled against 'Adud al-Dawla's authority. Mu'ayyad al-Dawla mobilized in support of 'Adud al-Dawla, forcing Fakhr al-Dawla to flee to the Ziyarids of Gorgan and Tabaristan. This did not stop the two Buyids; 'Adud al-Dawla took Gorgan in 980, while Mu'ayyad al-Dawla gained control of Tabaristan in 981. Mu'ayyad al-Dawla was entrusted with the newly captured provinces as 'Adud al-Dawla's subordinate.

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