Abstract: A Universe devoid of stars with masses exceeding 8-10 times that of the Sun would be barren of life as we know it. These so-called massive stars are not only the primary creators of elements essential for life, but they have also played a fundamental role in shaping the evolution of the Universe since the formation of the first stars. Although less abundant than their lower-mass counterparts, massive stars are crucial drivers of galaxy evolution. They influence the interstellar medium, star and planet formation through their intense ionizing radiation, powerful stellar winds, and final explosive fates as supernovae. In addition, they serve as beacons for studying the cosmos at distances of several million light-years. Moreover, even before their true nature was understood, massive stars have captivated humanity since the dawn of civilization.

Understanding the formation, evolution, and interactions of massive stars with their environments is a cornerstone of modern astrophysics. By the close of the 20th century, we believed we were on the verge of a comprehensive understanding of the physical processes governing their evolution. However, the advent of large-scale, high-resolution surveys of massive stars in various galaxies — particularly within the Local Group, including our own Milky Way — has revealed a much more complex picture than we initially anticipated. This complexity has underscored the need to reassess and refine our current paradigm of massive star evolution.

In this seminar, I will present several examples of the work undertaken by the IACOB team over the past 15 years, as part of broader global efforts within the massive star community, to reassemble the fragmented pieces of the massive star puzzle. Large-scale surveys have played a pivotal role in this ongoing effort, providing new insights and revealing the intricate details of massive star evolution that challenge previous models and assumptions.