Abu'l-Qasim al-Tayyib

Abū'l-Qāsim al-Ṭayyib ibn al-Āmir (أبو القاسم الطيب بن الآمر) was, according to the Tayyibi sect of Isma'ilism, the twenty-first imam. The only son of Caliph al-Amir bi-Ahkam Allah, al-Tayyib was an infant when his father was murdered. Amidst the ensuing power struggle, al-Tayyib disappeared; modern historians suggest that he died or was secretly killed by one of the rival strongmen. By 1132, his uncle al-Hafiz declared himself as the caliph and imam in succession to al-Amir. This was not accepted by the Yemeni Isma'ilis, who upheld the rights of al-Tayyib.

This marked the creation of two rival sects of Musta'li Isma'ilism, the Hafizi one, following al-Hafiz, and the Tayyibi one, following al-Tayyib. The Tayyibis hold that al-Tayyib was rescued from Cairo and brought to safety, but that he and all subsequent Tayyibi imams remained in concealment. The Tayyibi community has instead been led by a sequence of 'absolute missionaries' (da'i al-mutlaq).