Hasan (died September 976), better known by his laqab as Rukn al-Dawla (Persian: رکن‌الدوله دیلمی), was the first Buyid amir of northern and central Iran (c. 935–976). He was the son of Buya.

Hasan was the son of Buya, a Dailamite fisherman from Lahijan, who left his Zoroastrian faith and converted to Islam. Hasan had an older brother named 'Ali and a younger brother named Ahmad. He also had a sister named Kama.

In around 928, Hasan's brother 'Ali joined the services of Makan, who was the Samanid governor of Ray. 'Ali then managed to gain military positions for Hasan and their other brother Ahmad. At the time, Hasan was about thirty years old. When Makan attacked his Samanid overlords and was subsequently defeated by the Ziyarid prince Mardavij, the brothers transferred their allegiance to the latter.

In the following years, 'Ali repudiated his subservience to Mardavij and, after some time, managed to create an empire in Fars. During this time, Hasan distinguished himself in the battles over that province. Mardavij, however, marched south and forced 'Ali to recognize his authority in around 934. Hasan was sent to Madavij's court as a hostage. The death of Mardavij in 935 allowed Hasan to escape, and also provided an opportunity for the Buyids to expand into central Iran. 'Ali therefore sent Hasan to take Isfahan. The Ziyarids, now under Vushmgir, were busy dealing with the Samanids, allowing the Buyid to easily take the city. This success did not last, however. Internal disruptions, combined with an invasion by Vushmgir, forced Hasan to abandon Isfahan to the Ziyarids three years later. In 940, he appointed Abu 'l-Fadl ibn al-'Amid as his vizier.

Although he did not receive much support from 'Ali, Hasan continued to be involved in central Iran. In 940 he recaptured Isfahan, then defeated Vushmgir in battle and occupied Ray, which had been taken by the Samanids, in 943. Meanwhile, in 945 Hasan's brother Ahmad had managed to capture Baghdad, occupying the Abbasid Caliphate. The caliph al-Mustakfi gave Ahmad the honorific title of "Mu'izz al-Dawla", while 'Ali received the title of "'Imad al-Dawla". Hasan himself was bestowed with the title "Rukn al-Dawla".

That same year, 945, saw Rukn al-Dawla expelled from all of central Iran by Ibn Muhtaj, the governor of Samanid Khurasan. Only in 946 or 947 was he able to make his return to Ray. He was, however, able to expand his territory after doing so, stripping Vushmgir of Gurgan and Tabaristan. Some time later, Abu Mansur Muhammad, a former Samanid general who had rebelled against them, took refuge in Ray, and was honored by Rukn al-Dawla, who, along with his brothers, greatly awarded him with riches. Rukn al-Dawla shortly sent Abu Mansur to Damghan in order to protect Ray from an Samanid invasion.

In 948 or 949, the Sallarid ruler of Azerbaijan, al-Marzuban, became angry over a diplomatic insult sent to him by Mu'izz al-Dawla. He sought revenge against the Buyids by attempting to seize Ray from Rukn al-Dawla. The amir, however, convinced al-Marzuban by diplomatic measures to delay his expedition until his brothers sent him additional armies; he then sent an army under Abu Mansur which defeated al-Marzuban near Qazvin and imprisoned him.

In around 948 'Imad al-Dawla named Rukn al-Dawla's eldest son, Fana Khusrau ('Adud al-Dawla) as his successor. In September 949 he died, and Rukn al-Dawla claimed the title of senior amir for himself. He traveled to Shiraz and stayed there for at least nine months in order to secure his son's succession there, despite the fact that the Samanids were threatening his own possessions. Mu'izz al-Dawla, meanwhile, accepted Rukn al-Dawla's position of senior amir and also sent troops to Shiraz to assist 'Adud al-Dawla.