The Other God: Dualist Religions from Antiquity to the Cathar Heresy (Yale Nota Bene);

This fascinating book explores the evolution of religious dualism, the doctrine that man and cosmos are constant battlegrounds between forces of good and evil. It traces this evolution from late Egyptian religion and the revelations of Zoroaster and the Orphics in antiquity through the Dead Sea Scrolls, the Mithraic Mysteries, and the great Gnostic teachers to its revival in medieval Europe with the suppression of the Bogomils and the Cathars, heirs to the age-long teachings of dualism. Integrating political, cultural, and religious history, Yuri Stoyanov illuminates the dualist religious systems, recreating in vivid detail the diverse worlds of their striking ideas and beliefs, their convoluted mythologies and symbolism.  
Reviews of an earlier edition:
“A book of prime importance for anyone interested in the history of religious dualism. The author€s knowledge of relevant original sources is remarkable; and he has distilled them into a convincing and very readable whole.€-Sir Steven Runciman

“The most fascinating historical detective story since Steven Runciman€s Sicilian Vespers.€-Colin Wilson

“A splendid account of the decline of the dualist tradition in the East . . . both strong and accessible. . . . The most readable account of Balkan heresy ever.€-Jeffrey B. Russell, Journal of Religion 

“Well-written, fact-filled, and fascinating . . . has in it the making of a classic.€
-Harry T. Norris, Bulletin of SOAS