Al-Mansur al-Husayn (1669 - 1720) was an Imam over parts of Yemen, who ruled in rivalry with other competitors in 1716 - 1720. He belonged to the Qasimid family who dominated the Zaidi imamate of Yemen in 1597 - 1962.
Al-Husayn bin al-Qasim was a grandson of the imam al-Mu'ayyad Muhammad I (d. 1644). He took advantage of popular discontent with the current imam al-Mahdi Muhammad. He claimed the imamate in the strong fortification Shaharah in 1716, taking the name al-Mansur. A large part of the country quickly fell away from the unpopular al-Mahdi Muhammad. The old imam released his nephew al-Qasim from prison and sent him to deal with the pretender. However, al-Mansur al-Husayn defeated his opponent at As Sudah. Al-Qasim soon defected from his uncle, acknowledged al-Mansur al-Husayn, and besieged the old imam. Al-Mahdi Muhammad had to give up and sue for a truce. Al-Mansur al-Husayn began to strike coins in his own name. However, already in the same year 1716 a-Qasim turned against the new imam, and proclaimed himself with the name al-Mutawakkil al-Qasim. He controlled San'a and the seaports, while al-Mansur al-Husayn merely held Shaharah and some surrounding territories. Blocked from the sources of revenue, he led a meagre existence until he died in 1720.[1]