Like his elder brother and predecessor al-Mu'ayyad Ahmad, Abu Talib Yahya was a prominent man of learning and a descendant of Imam Hasan bin Ali. He succeeded al-Mu'ayyad Ahmad in the imamate of the Zaidi territories in Gilan and Deylaman in Persia, formally as "caliph".[1] At this time there were two major Zaidi territories, namely the area south of the Caspian Sea and the highlands of Yemen. For many years after the death of imam al-Mahdi al-Husayn in 1013, no local imam was appointed in the Yemeni territory.