It is 1250, and Brother Ranier, a middle-aged Preacher and former dualist heretic from Piacenza (Lombardy), writes a treatise about his former fellow believers, the Cathars. Following Ranier himself, who shaped his identity as an ex-heresiarch and later Brother Preacher, my approach to this subject takes into account Ranier and his work together, and considers that in anybody's life experience both past and present contribute to building up a whole individual, and that this individual's writings are necessarily – at least to some extent – the expression of this entirety. In other words, this ex-heretic turned-inquisitor wrote about his former companions not only as a convert who hid the acrimony and resentment typical of an apostate, but also as an inquisitor, bringing his own life, experience and problematic past into his textual construction of the heretical ‘adversary’.

Ranier's work, of little literary but enormous historical value, enjoyed great success – nineteen manuscripts containing all, or excerpts of, the Summa have been counted in the most recent survey by Käppeli, scattered throughout Europe. This is a telling figure, especially if compared to the two works most closely related to the Summa: the treatise attributed to Peter of Verona (1230–8) – known through two manuscripts – and Anselm of Alessandria's Tractatus (1267–70), of which only one version is extant. (The nature of the connection between these works will be discussed below.) Ranier's popularity is confirmed also by his frequent contacts with the papacy after his conversion: three different pontiffs (Innocent IV, Urban IV and Alexander IV) wrote to him frequently in the decade 1252–62, addressing their letters to him personally (‘to my beloved son in God Ranier, inquisitor in Lombardy’).

What surprised me most, however, is that Ranier does not feature equally prominently in his order's records and celebratory works.