Abu Ja'far al-Hajjaj ibn Ustadh Hurmuz was a Buyid general and governor.
[2][3] Thereafter Hajjaj was appointed as governor of Khuzistan, but his rule was marked by such arbitrariness that Baha al-Dawla replaced him in April/May 1001 by his brother, Hasan.
[1] Baha al-Dawla then appointed him as nazir and governor of Baghdad,[4] and charged him with the city's defence against an Uqaylid–Asadid alliance advancing on it under the command of Qirwash ibn al-Muqallad.
With the assistance of the Bedouin tribe of Banu Khafaja and the Kurdish Annazids, Hajjaj managed to rout the allies at Baziqiya.
[7][8] This angered Hajjaj, who defected with his followers to the Kurdish ruler Badr ibn Hasanwayh, and marched with him to lay siege to Baghdad in summer 1004.