Due to a lack of sources, the makers of customary law in the middle ages are largely unknown to us. However, a unique source, the Lois des pers du castel de Lille, makes it possible to identify the spokesmen of customary law courts, who were the intellectual authors of these courts' judgements and, thus, the main creators of customary law. An analysis of their careers shows that they were legal advisers, lords and/or bailiffs and members or spokesmen of other courts. In short, they were their community's legal experts. They had learned their trade by doing and can be considered to have been semi-professionals. Certain spokesmen were more successful than others and served as a court's main spokesman, but it is hard to determine why someone became the main spokesman or spokesman at all, though knights had more 'natural' authority for acting as spokesman than others. In fact, although the spokesmen formed a community of legal experts in their area, two subgroups (the knights and the others) can be distinguished. The case studied in this article concerns the spokesmen of a Flemish castellany court around 1300, but spokesmen can be found in Flanders already in 1122 and they were common in North-western Europe. Therefore, this article concludes with a call for further research about these key figures of medieval customary law.