Arabic Church Father and author of the seminal work Fountain of Knowledge. The text is divided into three parts: the philosophical ‘Dialectic’, the denunciatory ‘Concerning Heresy’ and the doctrinal ‘An Exact Exposition of the Orthodox Faith’. He didn’t let sex life go unmentioned, condemning its horrors in books on asceticism. In the period of iconoclasm he wrote three treatises defending the veneration of icons. Icons repaid him a hundredfold; when the caliph ordered his right hard to be cut off in response to slanderous rumours, John prayed so hard before an icon of the Blessed Virgin that his severed hand miraculously grew back.