The Buyid dynasty was founded by 'Ali ibn Buya, who in 934 conquered Fars and made Shiraz his capital, while his younger brother Hasan ibn Buya conquered parts of Jibal in the late 930s, and by 943 managed to capture Ray, which he made his capital. In 945, the youngest brother, Ahmad ibn Buya, conquered Iraq and made Baghdad his capital, receiving the honorific title of "Mu'izz al-Dawla" ("Fortifier of the State"), while 'Ali was given the title of "'Imad al-Dawla" ("Support of the State"), and Hasan was given the title of "Rukn al-Dawla" ("Pillar of the State").
As Daylamite Iranians the Buyids consciously revived symbols and practices of Iran's Sasanian Empire. In fact, beginning with 'Adud al-Dawla they used the ancient Sasanian title Shahanshah (شاهنشاه), literally "king of kings".
At its greatest extent, the Buyid dynasty encompassed most of today's Iran, Iraq, Kuwait, and Syria, along with parts of Oman, the UAE, Turkey, Afghanistan and Pakistan. During the 10th and 11th centuries, just prior to the invasion of the Seljuq Turks, the Buyids were the most influential dynasty in the Middle East, and under king 'Adud al-Dawla, became briefly the most powerful dynasty in the Middle East.
The word Būya (Arabic Buwayh) is a Middle Persian name ending in the diminutive ـویه (Middle Persian -ōē, modern Persian -ūya, Arabic -uwayh). The Buyids were descendants of Panah-Khusrau, a Zoroastrian from Daylam. He had a son named Buya, who was a fisherman from Lahijan, and later left Zoroastrianism and converted to Islam.:274 Buya later had three sons named Ahmad, 'Ali, and Hasan, who would later carve the Buyid kingdom together. Most historians agree that the Buyids were Daylamites.:251–52 The Buyids claimed royal lineage from Bahram V, 15th king of the Sasanian Empire.
The founder of the dynasty, 'Ali ibn Buya, was originally a soldier in the service of the Daylamite warlord Makan ibn Kaki, but later changed his adherence to the Iranian ruler Mardavij, who had established the Ziyarid dynasty, and was himself related to the ruling dynasty of Gilan, a region bordering Dailam. 'Ali was later joined by his two younger brothers, Hasan ibn Buya and Ahmad ibn Buya. In 932, 'Ali was given Karaj as his fief, and thus was able to enlist other Daylamites into his own army. However, 'Ali's independent actions made Mardavij plan to have him killed, but fortunately for 'Ali, he was informed of Mardavij's plan by the latter's own vizier. The Buyids brother, with 400 of their Daylamite supporters, then fled to Fars, where they managed to take control of Arrajan. However, the Buyids and the Abbasid general Yaqut shortly came into a struggle for the control of Fars, which the Buyids eventually emerged victorious in. This victory opened the way for the conquest of the capital of Fars, Shiraz.