A distinguished scholar, author, and statesman, al-Mu'ayyad fi'l-Din al-Shirazi (1000-1078 CE) lived during one of the most turbulent periods in Islamic history. The 11th century was characterized, among other things, by an acute struggle for supremacy between the Sunni and Shi'a branches of Islam, represented politically by the 'Abbasid and Fatimid caliphates. Al-Mu'ayyad was originally a Fatimid missionary; but his outstanding intellectual and literary skills eventually gained him important positions in the Fatimid administration. Eventually, he attained the highest ranks in the religious...