Our new era of gravitational wave astrophysics has opened an entirely new frontier for understanding black holes, from their birth in the early Universe to the supermassive monsters observed in all massive galaxies today. I will demonstrate how a new generation of industrial-scale time-domain surveys is creating a new multi-messenger view of supermassive black holes. The pioneering new SDSS-RM project uses light echoes to map the three fundamental quantities that describe astrophysical black holes: mass, spin, and growth rate. In the next decade, the new SDSS-V Black Hole Mapper and Rubin/LSST will map millions of supermassive black holes in light echoes, complementing the gravitational echoes seen soon in pulsar timing and (eventually) LISA. I will also discuss how Hubble Space Telescope spectroscopy can spatially resolve the fossil record of black hole seeds, as well as off-nuclear black holes leftover from recent galaxy mergers. Very soon, the first James Webb Space Telescope observations in the CEERS project will directly map the formation of the first black hole seeds in the early Universe. The next generation of multi-messenger experiments make it a truly bright time for understanding the dark nature of black hole astrophysics.