Pierre Renson passed away on 1 February, at the age of 91. He is best known in the “Ap & Related Stars” community for his “Catalogue of Ap, HgMn and Am stars” (published with Jaen Manfroid as co-author) and his collaboration with Franco Catalano for the “Catalog of Observed Periods of Ap Stars” and its various supplements. He has also published a significant body of original research, including in particular an analysis of HD 32633 that established for the first time in a convincing manner the occurrence of complex, strongly anharmonic variability of the mean longitudinal magnetic field in an Ap star. This study probably received less attention than it deserved as it was written in French, making it less accessible to a fraction of the community. Pierre Renson was still frequently going to the Institut d’Astrophysique in Liège until a few weeks before his death. Our thoughts at this time are with his children and grandchildren.