Astrophysical Lessons from LIGO-Virgo-KAGRA's Black Holes

The LIGO-Virgo-KAGRA detector network has observed over 70 gravitational-wave sources to date, including mergers between black holes, neutron stars, and mixed neutron star-black holes. Focusing on the black hole mergers, I will describe some recent lessons into how, when, and where black holes are made. These questions are connected to several astrophysical puzzles, including the deaths of massive stars, the growth of black holes across cosmic time, high-redshift star formation, and properties of globular clusters.