Question: Ubaydallah ibn Abdallah ibn Tahir was the last major Tahirid to hold high office in what dynasty?

full_context: Document 1: 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.
Document 2: 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.
Document 3: Khazim ibn Khuzayma al-Tamimi: Khazim ibn Khuzayma al-Tamimi (  749–768 ) was a Khurasani Arab military leader. One of the early supporters of the Abbasid "da'wa" in Khurasan, he played a major role in the Abbasid Revolution against the Umayyads, and then spent the next two decades suppressing revolts across the Caliphate. As one of the main figures of the "Khurasaniyya", the main power base of the Abbasid regime, he cemented his family in a position of power and influence: his sons would play an important role in the affairs of the Caliphate over the next decades.
Document 4: Hotak dynasty: The Hotak dynasty or the Hotaki dynasty was an Afghan monarchy of the Ghilji Pashtuns, established in April 1709 by Mirwais Hotak after leading a successful revolution against their declining Persian Safavid overlords in Kandahar. It lasted until 1738 when the founder of the Afsharid dynasty, Nader Shah Afshar, defeated Hussain Hotak during the long siege of Kandahar, and started the reestablishment of Iranian suzerainty over all regions lost decades before against the Iranian archrival, the Ottomans, and the Russians. At its peak, the Hotak dynasty ruled very briefly over an area which is now Afghanistan, western Pakistan, and large parts of Iran.
Document 5: Abu Muslim: Abu Muslim Abd al-Rahman ibn Muslim al-Khorasani or al-Khurasani (Arabic: أبو مسلم عبد الرحمن بن مسلم الخراساني‎ ‎ born 718-19 or 723-27, died in 755), born Vehzādān Pūr-i Vandād Hormoz (Persian: وهزادان پور ونداد هرمزد‎ ‎ ), was a Persian general in service of the Abbasid dynasty, who led the Abbasid Revolution that toppled the Umayyad dynasty.
Document 6: Abna' al-dawla: The abnāʾ al-dawla (meaning "sons of the regime/dynasty"), often simply " the "Abnāʾ"", is a term for the Khurasani Arabs who had participated in the Abbasid Revolution of 749–750 and their descendants, who settled in Baghdad and Iraq. They became the ruling elite of the Abbasid Caliphate and formed the mainstay of the caliphal army. However, the term appears rarely in the sources until the time of the Fourth Fitna civil war in the 810s, when it is applied to the Khurasanis of Baghdad, who overwhelmingly supported Caliph al-Amin against his brother al-Ma'mun. The terms "ahl Khurāsān" ("people of Khurasan") and "abnāʾ ahl Khurāsān" ("sons of the people of Khurasan") are more frequently used for the Khurasanis who formed the mainstay of the Abbasid regime in general. Following al-Ma'mun's victory in the civil war, the "abnāʾ al-dawla" were largely replaced by the latter's Persian followers, and under his successor al-Mu'tasim, the rise of the Turkish slave-soldiers to power began.
Document 7: Amr ibn Ubayd: Amr Ibn Ubayd ibn Bāb (Arabic: عمرو بن عبيد بن باب‎ ‎ , died 761) was one of the earliest leaders in the "rationalist" theological movement of the Mu'tazilis, literally 'those who withdraw themselves' - which was founded by Wasil ibn Ata (died 749). A student of the famous early theologian Hasan al-Basri, he led the Mutazilis during the early years of the Abbasid caliphate. He generally followed a quietist political stance toward the Abbasid political establishment.
Document 8: Muttalib ibn Abdallah ibn Malik: 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.
Document 9: Muhammad ibn Abdallah ibn Tahir: 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.
Document 10: Ibn Khordadbeh: 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.
Document 11: 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.
Document 12: Ishaq ibn Ibrahim al-Mus'abi: 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.
Document 13: Muhammad ibn Mikal: 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.
Document 14: Anarchy at Samarra: The term "Anarchy at Samarra" refers to the period 861–870 in the history of the Abbasid Caliphate, which was marked by extreme internal instability and the violent succession of four caliphs, who became puppets in the hands of powerful rival military groups. The term derives from the then capital and seat of the caliphal court, Samarra. The "anarchy" began in 861, with the murder of Caliph al-Mutawakkil by his Turkish guards. His successor, al-Muntasir, ruled for six months before his death, possibly poisoned by the Turkish military chiefs. He was succeeded by al-Musta'in. Divisions within the Turkish military leadership enabled Musta'in to flee to Baghdad in 865 with the support of some Turkish chiefs (Bugha the Younger and Wasif) and the Tahirids, but the rest of the Turkish army chose a new caliph in the person of al-Mu'tazz and besieged Baghdad, forcing the city's capitulation in 866. Musta'in was exiled and executed. Mu'tazz was able and energetic, and tried to control the military chiefs and exclude the military from civil administration. His policies were resisted, and in July 869 he too was deposed and killed. His successor, al-Muhtadi, also tried to reaffirm the Caliph's authority, but he too was killed in June 870. With Muhtadi's death and the ascension of al-Mu'tamid, the Turkish faction around Musa ibn Bugha, closely associated with Mu'tamid's brother and regent al-Muwaffaq, became dominant in the caliphal court, ending the "anarchy". Although the Abbasid Caliphate was able to stage a modest recovery in the following decades, the troubles of the "Anarchy at Samarra" inflicted great and lasting damage on the structures and prestige of the Abbasid central government, encouraging and facilitating secessionist and rebellious tendencies in the Caliphate's provinces.
Document 15: Sulayman ibn Abdallah ibn Tahir: 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.
ground_truth: Tahirid dynasty