This book is a comparative study of two major Shii thinkers Hamid al-Din Kirmani from the Fatimid Egypt and Mulla Sadra from the Safavid Iran, demonstrating the mutual empowerment of discourses on knowledge formation and religio-political authority in certain Ismaili and Twelver contexts. The book investigates concepts, narratives, and arguments that have contributed to the generation and development of the discourse on the absolute authority of the imam and his representatives. To demonstrate this, key passages from primary texts in Arabic and Persian are translated and closely analyzed to highlight the synthesis of philosophical, Sufi, theological, and scriptural discourses. The book also discusses the discursive influence of Nasir al-Din Tusi as a key to the transmission of Ismaili narratives of knowledge and authority to later Shii philosophy and its continuation to modern and contemporary times particularly in the narrative of the guardianship of the jurist in the Islamic Republic of Iran.