Ubaydallah ibn Abdallah ibn Tahir was the last major Tahirid to hold high office in what dynasty?
Tahirid dynasty The Tahirid dynasty (Persian: طاهریان‎ ‎ , "Tâhereyân") was a dynasty, of Persian dihqan origin, that governed the Abbasid province of Khorasan from 821 to 873 and the city of Baghdad from 820 until 891. The dynasty was founded by Tahir ibn Husayn, a leading general in the service of the Abbasid caliph al-Ma'mun. Their capital in Khorasan was initially located at Merv but was later moved to Nishapur. The Tahirids enjoyed a high degree of autonomy in their governance of Khorasan, but they remained subject to the Abbasid caliphate and were not independent rulers.
Abdallah ibn Ali Abdallah ibn al-Abbas (ca. 712 – 764 CE) was a member of the Abbasid dynasty, who played a leading role in its rise to power during the Abbasid Revolution. As governor of Syria, he consolidated Abbasid control over the province, eliminating the remnants of the Umayyad dynasty and suppressing pro-Umayyad uprisings. After the death of his nephew and first Abbasid Caliph, al-Saffah, in 754, he launched a bid for the caliphal title against al-Saffah's brother, al-Mansur, but was defeated and imprisoned. He was killed in 764.