Krzysztof (Chris) Belczynski pioneered the study of massive black hole formation from the collapse of metal-poor progenitors, several years before the advanced detectors' era. He demonstrated that binary population synthesis is the necessary starting point to understand the (astro)physics of binary compact objects, unraveling the importance of stellar winds, mass transfer, and common envelope. Thanks to his work, we understand why LIGO and Virgo have observed many more binary black holes than neutron star mergers. For many years to come, his models will be a cornerstone for the science case of the Einstein telescope, as well as for the other implications of massive binary star evolution across cosmic time. His volcanic, unconventional, and provocative personality will be sorely missed.