Matteo Cantiello, an astrophysicist at the Flatiron Institute, lectures at the Institute for Advanced Study's Wolfensohn Hall on how black holes form and behave inside stars across a wide range of masses. He works through stellar evolution models to show what happens when a black hole forms in the core of a massive star or when one is captured inside a stellar envelope, tracing the observable consequences for luminosity, mass loss, and eventual collapse. The talk connects theoretical predictions from stellar structure calculations to what telescopes and gravitational wave detectors actually see, covering stellar-mass black holes formed in supernovae as well as scenarios relevant to intermediate and more exotic mass ranges. Cantiello frames open questions about which massive stars leave black holes behind, how common black hole-star binaries might be, and what signatures would confirm a black hole buried inside a still-living star. The lecture assumes familiarity with stellar astrophysics and gravitational physics.