Hasan ibn Zayd Al - Ḥasan ibn Zayd ibn Muḥammad ibn Ismā ‘ il ibn al - Ḥasan ibn Zayd ( ; died 6 January 884 ) , also known as al - Da ‘ ī al - kabīr ( , " the Great / Elder Missionary " ) , was an Alid who became the founder of the Zaydid dynasty of Tabaristan . Biography . Hasan was a descendant of Hasan ibn Zayd ibn Hasan , a great - grandson of Ali , the son - in - law of Muhammad and fourth Caliph . In 864 , he was living at Rayy in northern Iran , when he was invited by pro - Alid elements in the neighbouring province of Tabaristan to join them in an uprising against the Abbasid authorities . Tabaristan , a mountainous region on the southern shore of the Caspian Sea , had remained largely untouched by the Muslim conquests of the 7th century . Until conquered by the Abbasid Caliphate in 759 / 60 , it had been ruled by a native Persia n dynasty , the Dabuyids , and even after the imposition of direct Muslim rule local dynasties retained a large measure of autonomy in the mountainous interior . It was only after 840 , when Tabaristan came under Tahirid rule ( the Abbasids ' viceroys for the East ) , that the Islamization of the province began . It proceeded rapidly , and although the majority of the people adopted Sunni Islam , the province offered opportunities for the activities of pro - Alid Shi ' ite missionaries as well . In the 860s , western Iran was governed by the Tahirid Muhammad ibn Abdallah ibn Tahir , whose brother Sulayman ibn Abdallah ibn Tahir deputized him in Tabaristan and Gurgan . Popular resentment of the Tahirids ' rule increased through the oppression of their officials , especially their fiscal agents in the province . Consequently , in 864 a rebellion broke out in the towns of Ruyan , Kalar and Chalus , led by two " sons of Rustam " . The rebels called upon Hasan to lead them , and allied themselves with the neighbouring Daylam ites . Hasan , who assumed the regnal name al - Da ‘ ī ila ’ l - ḥaqq ( " He who summons to the Truth " ) , was recognized as emir by a part of the local population , and even secured the allegiance of the Justanid king of Daylam , Vahsudan ibn Marzuban . Despite the rapid success of the rebellion , Hasan ' s reign was troubled due to repeated invasions , and he was several times forced to seek refuge in Daylam . Thus he was chased out of Tabaristan in 865 by Sulayman ibn Abdallah , but returned within the same year and recovered the province . Another Alid uprising occurred in Qazvin and Zanjan in 865 , led by Husayn ibn Ahmad al - Kaukabi and aided by the Justanids , but it was suppressed two years later by the Abbasid general Musa ibn Bugha . Hasan was forced into Daylam again by the Abbasid general Muflih in 869 , but he withdrew shortly after . In 874 , Hasan came into conflict with Ya ' qub al - Saffar for sheltering one of the latter ' s enemies , Abdallah al - Sijzi . Ya ' qub invaded Tabaristan and defeated the Zaydid forces at Sari , forcing Hasan once again to flee to the mountains of Daylam . Nevertheless , Ya ' qub ' s army soon became bogged down by torrential rainfall and suffered many casualties to disease in the unaccustomed subtropical climate of Tabaristan , forcing him to withdraw from the region shortly after . In the complex struggle for control of Khurasan between Abu Talha Mansur ibn Sharkab and Ahmad ibn Abdallah al - Khujistani , Hasan sided with the former , but was defeated with him in 878 / 879 , when al - Khujistani recovered Nishapur . Utilizing the turmoils of the period , from 867 Hasan also usually controlled Gurgan to the east , and expanded his control temporarily over some neighbouring regions as well : Rayy ( 864 – 865 , 867 , 870 and 872 ) , Qazvin ( 865 – 868 ) and Qumis ( 873 – 879 ) . Hasan died at Amul in 884 , and was succeeded by his brother Muhammad ibn Zayd . The Zaydids continued to rule Tabaristan until 928 . Historians praised him as a just and equitable ruler , but outside the early strongholds of Ruyan and Kalar , the initial enthusiasm for his rule seems to have waned quickly among the broad populace of Tabaristan and Gurgan . This was a result of both his ardent enforcement of Shi ' ism and repression of the Sunni majority , as well as his regime ' s reliance on the semi - barbarous Daylamite soldiery . Relations with the autonomous local Iranian rulers also varied : the Qarinids , who ruled the western mountains of Tabaristan , supported Hasan , but the Bavandids in the eastern mountains were usually hostile , and relations with the Justanid Vahsudan and his son and successor Khurshid also turned hostile . In the event , hasan managed to have the latter replaced by his brother Justan , who once again loyally supported the Zaydid ruler . The Orientalist Frants Buhl assesses Hasan ' s character thus : he " possessed rare energy and the capacity for stubborn resistance , was a sincerely religious man , well educated , and a patron of letters " .