Sergio Dain passed away in February 2016, at the early age of 46. He was a full proffesor at the National University of Córdoba (Argentina) and worked for several years at the Max-Planck Institut für Gravitationsphysik, Albert Einstein Institut (AEI). Sergio was an impressive young scientist. His natural kindness, as well as his enthusiasm, passion and commitment towards any knowledge related activity made him unforgettable for anyone fortunate to met him. Sergio was among the first to join the Editorial Board of Papers in Physics and always contributed to our endeavour generously and enthusiastically.