Eminent Twelver/Ithna Ashari/Imami Shii theologian, jurist, traditionist, bibliographer, and Quran commentator from the Iranian province of Khurasan. Compiled two of the four canonical books of Twelver traditions. Made major contributions to the structuring of a Twelver system of jurisprudence and theology independent of the imam during the critical century following the Great Occultation (the disappearance of the last imam, 940). Sought a middle ground between rationalism and traditionalism. Known as Shaykh al-Taifah, “master of the sect,” for his definitive collections of hadith as well as his index of Shii works (fihrist) and numerous other works.