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.
Al-Mu'tasim Abū Isḥāq Muḥammad ibn Hārūn al-Rashīd (Arabic: أبو إسحاق محمد بن هارون الرشيد‎ ‎ ; October 796 – 5 January 842), better known by his regnal name al-Muʿtaṣim bi’llāh (المعتصم بالله , "he who seeks refuge in God"), was the eighth Abbasid caliph, ruling from 833 to his death in 842. A younger son of Harun al-Rashid, he rose to prominence through his formation of a private army composed predominantly of Turkish slave-soldiers ("ghilmān"). This proved useful to his half-brother, Caliph al-Ma'mun, who made use of al-Mu'tasim and his Turkish guard to counterbalance other powerful interest groups in the state, as well as employing them in campaigns against rebels and the Byzantine Empire. When al-Ma'mun died unexpectedly on campaign in August 833, al-Mu'tasim was thus well placed to succeed him, overriding the claims of his nephew, al-Abbas ibn al-Ma'mun.