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.
Al-Mu'tadid Abu'l-Abbas Ahmad ibn Talha al-Muwaffaq (854 or 861 – 5 April 902), better known by his regnal name al-Mu'tadid bi-llah (Arabic: المعتضد بالله‎ ‎ , "Seeking Support in God" ) was the Abbasid Caliph in Baghdad from 892 until his death in 902.