Charles the Bold's relations with the republic of Florence — and with the successive heads of the city's de facto ruling family, the Medici, Piero (1464–1469) and his son Lorenzo (1469–1492) — were rather different in kind from those he maintained with the other major secular powers of Italy, and this accounts for their treatment here in a separate chapter. Diplomatically, these relations were always distant. Both the republic and the Medici family itself had long enjoyed close, almost dependent, links with the French crown, and it was mainly for this reason that Florence, alone of the four major secular states in the peninsula, never made an alliance with Charles. Economically, however, the ties between Florence and Valois Burgundy were much closer. Moreover, the Medici had a financial link with Burgundy on their own account, through the establishment in 1439 of a subsidiary branch of their bank in Bruges. The significance of these economic ties was increased by the fact that they inevitably took on a political dimension. For example, the Medici bank had subsidiary branches not only in Bruges but also in Lyon and London, and economic considerations played a large part in deciding the attitude adopted by both the Medici and the Florentine republic towards Burgundy and France. Again, Tommaso Portinari, the manager of the Bruges bank during the reign of Charles the Bold, was one of the most prominent of the many Italians who frequented his court, and, because Florence accredited no ambassador to Burgundy, Portinari was occasionally called upon to act in a quasi-diplomatic capacity on behalf of the republic or of the Medici.

The importance of the career of Tommaso Portinari justifies the emphasis implied in the title of this chapter. The concentration on one man is explained also by the fact that Portinari's political and economic activities during Charles the Bold's reign have never been fully studied together, so that some aspects still remain controversial: for example, the extent and wisdom of his financial links with the duke himself. At the same time, it should be remembered that he served not one but two masters: the Medici, as manager of the Bruges bank, and the duke, as councillor.