Ubaydallah ibn Abdallah ibn Tahir was the last major Tahirid to hold high office in what dynasty?
Ubaydallah ibn Abdallah ibn Tahir Abu Ahmad Ubaydallah ibn Abdallah ibn Tahir (Arabic: أبو أحمد عبيد الله بن عبد الله بن طاهر‎ ‎ , ca. 838 – May 913) was a ninth century Tahirid official and military officer. He was the last major Tahirid to hold high office, having served as the governor of Baghdad at various points between 867 and 891.
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.