Book excerpt: This accessible biography treats al-Ma'mum (786-833) as the product of his age, which was a formative period in the development of Islamic law and theology. It presents him in his many facets: rebel, rationalist, scientist, poet, politician, warrior, inquisitor, and self-proclaimed defender of the faith. Drawing on contemporary sources, some friendly and others hostile, it offers a comprehensive portrait of a fascinating figure in Islamic history.