A biographical approach to Bertomeu de Tresbens, a physician and astrologer who worked for King Pere el Cerimoniós of Aragon and for his son infant Joan, later known as Joan I el Caçador. This biography is built on a thorough reseach based on all documentation on him found in archives -principally in the Archive of the Crown of Aragon-, as well as on the information contained in all his astrology works. We place Tresbens in his Occitan origin and in the economic, political and social contexts of the time when he had been documented in territories of the Crown of Aragon. Thus, the man behind the most important Catalan oeuvre on astrology is brought to light. We have studied particularly his career regarding his relationship with the monarchy and with the town of Cervera, whose local government planned to employ him as a physician. Finally, we present an original edition of all documentation found in archives regarding Tresbens used in this paper.