Al-Qasim bin al-Husayn was a grandson of Imam
al-Mahdi Ahmad (d. 1681), and the nephew of Imam
al-Mahdi Muhammad (d. 1718). During the reign of his uncle, he was a military commander of note, and chastised the
Hashid tribes in 1707. For some time he was imprisoned by the ruler. In 1716, however, al-Mahdi Muhammad was badly cornered by the rival imam
al-Mansur al-Husayn. He therefore released al-Qasim and sent him to fight the pretender. At Sudah, al-Qasim was defeated by the latter. He subsequently fell out with al-Mahdi Muhammad and submitted to al-Mansur al-Husayn. He proceeded to besiege his uncle on behalf of the pretender imam, and forced him to plead for a truce. However, al-Qasim had no intention to stick to al-Mansur al-Husayn. In the same year 1716 he rose against the usurper and proclaimed himself imam under the name al-Mutawakkil al-Qasim. Since he controlled
San'a and the seaports, he was able to block the revenues of al-Mansur al-Husayn, who was ensconced in Shaharah and whose powers were rapidly dwindling. When al-Mansur al-Husayn died in 1720, the Zaidi state was firmly in al-Mutawakkil al-Qasim's hands. ==Reign==