The Libro dei Conti of the Venetian merchant Giacomo Badoer who lived in Constantinople from 1436 to 1440 makes frequent mention of a strange figure referred to as '[Chir] Todaro Vatazi [patron de nave de Chandia] [chomerchier di pesi].' In fact Badoer here speaks of of two different persons named Theodore Batatzes: the one a Cretan shipowner (ob. 1439), the other a Byzantine 'chomerchier di pesi.' Venetian notarial documents from Crete allow us to distinguish the activitiy of each and, more particularly, to trace the career of the Byzantine Kyr Theodoros Batatzes, attested as a commercial agent and benefactor of an Athonite monastery until 1449. The problem posed by these identical names, complicated further by a third contemporary Theodore Vatatzes, is studied in connexion with the diffusion of the family name Vatatzes in the Greek-speaking territory subject to various political authorities in the fifteenth century. Finally, the office of 'chomerchier di pesi' is discussed, drawing on our meagre sources for the Byzantine financial system on the eve of the fall of Constantinople.