Black holes are among the most enigmatic and powerful objects in the cosmos, lurking at the centers of nearly all massive galaxies. Yet, their growth and their intricate interplay with their host galaxies remain key mysteries in astrophysics. In this talk, I will present results from cutting-edge cosmological hydrodynamic simulations that track the evolution of galaxies and their central black holes from the early Universe to the present day. We will uncover how gas flows across cosmic time to feed black holes, and how the resulting feedback can regulate or even shut down star formation. I will also take you inside the world of supercomputer simulations—how we model such extreme processes and connect them to astronomical observations. Along the way, we will explore why some of the most seemingly quiescent galaxies may conceal the most turbulent episodes of black hole activity, and what the next generation of telescopes and simulations will reveal about these cosmic engines.