Abu Taher was the Buyid ruler of Hamadan from 997 to 1021. He was the son of Fakhr al-Daula. Fakhr al-Daula died in 997; his elder son Abu Taleb Rostam ("Majd al-Daula") took power in the bulk of his father's possessions in Jibal. Abu Taher himself gained the governorships of Hamadan and Kirmanshah, and was hence known as Shams al-Daula. Since both sons were still minors their mother, the "Sayyida", assumed the regency. Wikipedia
The definitive Wikipedia entry for Shams Al-Daula. Wikipedia is the biggest multilingual free-content encyclopedia on the Internet. en.wikipedia.org/wiki/Shams_al-Daula