The aim of this contribution is to introduce Iudex Perfectus (1662), a little-known treatise on the qualities of the judge, and its writer, Gabriel Álvarez de Velasco, who had been a judge himself. It elaborates on the structure of the work and on the matter treated in relation to its subject, being the qualities of the good judge, with a focus on corruptibility. As this contribution is part of an ongoing research project, it hopes to yield a provisionary image of Álvarez de Velasco’s definition of the good judge.