Question: Ubaydallah ibn Abdallah ibn Tahir was the last major Tahirid to hold high office in what dynasty?
Context: Abu'l-Abbas Muhammad ibn Abdallah ibn Tahir (824/5 – November 867) was a Tahirid who served the Abbasid Caliphate as governor and chief of police ("sahib al-shurta") of Baghdad from 851 until his death, during a particularly troubled period in the city's history, which included its siege during the civil war of 865–866, in which he played a major role.  He also served in the 860s as governor of Iraq, Mecca and Medina, and was noted as a scholar, a poet and a patron of artists and scholars. Sulayman ibn Abdallah ibn Tahir (Arabic: سليمان بن عبد الله بن طاهر‎ ‎ ) was a ninth century Tahirid official in the service of the Abbasid Caliphate.  He was the last Tahirid governor of Tabaristan, ruling there until he was expelled by the rebellion of al-Hasan ibn Zayd in 864, and was afterwards appointed governor of Baghdad and the Sawad in 869, a position which he held until his death in 879. 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. Abu al-Hasan Ali ibn Abbas ibn Jurayj (Arabic: أبو الحسن علي بن العباس بن جريج‎ ‎ ), also known as Ibn al-Rumi (born Baghdad in 836; died 896), was the son of a Persian mother.  By the age of twenty he earned a living from his poetry, which would culminate in his masterpiece "Diwan".  His many political patrons included the Tahirid ruler Ubaydallah ibn Abdallah ibn Tahir, Abbasid Caliph Al-Mu'tamid's minister the Persian Isma'il ibn Bulbul, and the politically influential Nestorian family Banu Wahb.  He was a Shiite with Mutazilite leanings.  He died of illness at the age of 59 although some have suggested that poison or suicide may have been the cause. Muhammad ibn Mikal was an Iranian nobleman from the Mikalid family, who served as a military commander of the Tahirid dynasty.  He was the son of Mikal, a nobleman who had left Iraq and settled in Khurasan, and could trace his descent back to the Sogdian ruler Divashtich.  Muhammad also had a brother named Shah ibn Mikal, who, during his early career, along with Muhammad, played an important role under the Tahirid ruler Abdallah ibn Tahir al-Khurasani.  In 864, the Alid Hasan ibn Zayd conquered Tabaristan from the Tahirids, while another Alid named Muhammad ibn Ja'far ibn al-Hasan expelled the Tahirid governor of Ray, and captured the city.  The Tahirid ruler Muhammad ibn Tahir shortly sent an army from Khurasan under Muhammad ibn Mikal, who managed to recapture the city and capture Muhammad ibn Ja'far.  Hasan, however, quickly made a counter-attack under his Dailamite general Wajin, who managed to rout the army of Muhammad ibn Mikal, and kill the latter. Ali ibn Abu'l-Hayja 'Abdallah ibn Hamdan ibn al-Harith al-Taghlibi (Arabic: سيف الدولة أبو الحسن ابن حمدان‎ ‎ ), more commonly known simply by his "laqab" (honorific epithet) of Sayf al-Dawla ("Sword of the Dynasty"), was the founder of the Emirate of Aleppo, encompassing most of northern Syria and parts of western Jazira, and the brother of al-Hasan ibn Abdallah ibn Hamdan (better known as Nasir al-Dawla). Abu'l-Qasim Ubaydallah ibn Abdallah ibn Khordadbeh (Persian: ابوالقاسم عبیدالله ابن خردادبه‎ ‎ ) (c. 820 – 912 CE), better known as Ibn Khordadbeh or Ibn Khurradadhbih, was the author of the earliest surviving Arabic book of administrative geography.  He was a Persian geographer and bureaucrat of the 9th century.  He was the son of Abdallah ibn Khordadbeh, a prominent Abbasid general, who was the son of a Zoroastrian convert to Islam.  Ibn Khordadbeh was appointed "Director of Posts and Intelligence" for the province of Jibal in northwestern Iran under the Abbasid Caliph al-Mutammid (ruled 869–885 CE).  In this capacity ibn Khordadbeh served as both postmaster general and the Caliph's personal spymaster in that vital province. Muttalib ibn Abdallah ibn Malik al-Khuza'i was a son of the Abbasid general and administrator Abdallah ibn Malik al-Khuza'i.  During the civil war between al-Amin and al-Ma'mun, he sided with the latter.  In 811, he administered the oath of allegiance ("bay'ah") to al-Ma'mun for Mosul, and was named governor of Egypt briefly in 813 and again in 814–816.  In 817, however, after al-Ma'mun chose the Alid Ali al-Rida as his heir, Muttalib joined the uprising in Baghdad against al-Ma'mun, and even administered the oath to the city's rival Caliph, Ibrahim ibn al-Mahdi. Abu al-Husayn Ishaq ibn Ibrahim (Arabic: أبو الحسين إسحاق بن إبراهيم‎ ‎ , died July 850) was a ninth-century official in the service of the Abbasid Caliphate.  A member of the Mus'abid family, he was related to the Tahirid governors of Khurasan, and was himself a prominent enforcer of caliphal policy during the reigns of al-Ma'mun, al-Mu'tasim, al-Wathiq, and al-Mutawakkil.  In 822 he was appointed as chief of security ("shurtah") of Baghdad, and over the next three decades he oversaw many of the major developments in that city, including the implementation of the "mihnah" or inquisition, the removal of the Abbasid central government to Samarra, and the suppression of the attempted rebellion of Ahmad ibn Nasr al-Khuza'i.  After his death, the "shurtah" of Baghdad briefly remained in the hands of his sons, before being transferred to the Tahirid Muhammad ibn 'Abdallah ibn Tahir in 851. 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.
Answer: Tahirid dynasty