CASTRO, JUAN de. - Carthusian ascetical writer, born in Toulouse in 1485 to an illustrious family, died at the age of 72 on 6 July 1556. Sent by his father to the University of Paris, he not only obtained his degree there, but also held the chair of theology. Among his most assiduous disciples was Ignazio di Loyola, who had come to Paris in 1528. The professor became closely attached to him in friendship, and while he instilled in his disciple the principles of sacred learning, the pupil, already a master of spirituality, developed the most sublime ascetical theses. He relinquished his chair, returned to Spain, and on 13 June 1535 entered as a novice at the Charterhouse of Val di Cristo, where, after a few months, Ignazio came to visit him and revealed to him his plan of founding the Society of Jesus. Having professed religious vows on 24 June 1536, he was shortly afterwards appointed prior of the Charterhouse of Val di Cristo, and later prior of that of Porta Coeli.
He wrote the treatise De inenarrabilibus Christi doloribus, quos moriens sponte pro nobis tulit. His letters were preserved as sacred objects in the Charterhouse of Val di Cristo (Acta SS. Iulii, VII, Paris 1868, Comment. praecius ad acta S. Ignatii, no. xx).