Zoom info: https://stanford.zoom.us/j/423773826

I will provide an overview of our quest to understand, with theory and observations, undetected populations of black holes, proceeding from the nearby to the faraway Universe. First, I will unveil a new extensive, multiwavelength observational campaign likely leading to the discovery of the second closest supermassive black hole, located in the Milky Way satellite Leo I. I will then describe some orbital and radiative properties of intermediate-mass black holes potentially wandering in local galaxies, including the Milky Way. Moving higher in the redshift ladder, I will detail the detection of the farthest lensed quasar to date and theoretical arguments as to why we are missing a significant fraction of this population. Still in the reionization epoch, I will delineate the discovery of two candidate galaxies at redshift z > 10 and the possibility that they host supermassive black holes. I will then conclude with the observational properties of the same sources that have started the reionization at z ~ 30: the first population of stars and black holes, and how we may soon be able to detect them directly.