Almost everything we know about the Universe beyond our Earth stems from the light of stars. To decode the information that is imprinted in this light, we need to understand its origin in the outermost layers of the stars, the so-called "stellar atmosphere". Only a realistic physical model of these transition layers allows us to translate our observations into a proper understanding of stars. Consequently, stellar atmosphere models are a fundamental tool of modern astrophysics. In the massive star regime, Wolf-Rayet stars are a rare but important class of stars. A large fraction of Wolf-Rayet stars contains no or only a small amount of hydrogen, thereby providing a crucial benchmark for the late evolution of massive stars before collapsing into massive black holes. With mass-loss rates that are about ten times higher than those of O supergiants, just a few Wolf-Rayet stars are enough to easily outweigh the feedback of a whole population of OB stars. To properly understand and quantify the impact of Wolf-Rayet and other massive stars, their spectra need to be analyzed with the help of stellar atmosphere models. Located at the conjunction of theory and observation, my new Emmy Noether group at the ARI will investigate the parameters and impact of hot and massive stars with various approaches revolving around the use of current and next-generation stellar atmospheres. The seminar talk will provide an overview of the techniques and challenges of modern atmosphere models as well as outline the underlying concept for including a consistent hydrodynamic treatment. Focusing on the yet poorly understood winds of Wolf-Rayet stars, I will show recent results from a groundbreaking study of massive He-star atmosphere models, yielding the very first mass-loss recipe derived from first principles in this regime. With major consequences on e.g. maximum black hole masses or He II ionising fluxes, I will outline the importance of making progress in the field of stellar atmospheres and give a brief outlook on some of the core questions the new research group will address.