Distant quasars observed less than one billion years after the Big Bang are ideal tracers for studying the birth of the earliest supermassive black holes, the assembly of the first massive galaxies, and the buildup of the large-scale structures seen in the early Universe. The PIs will perform a detailed characterization of 25 such quasars by analyzing a legacy multi-wavelength dataset collected from the world's largest telescopes, covering a wavelength range from X-ray to radio. This program will advance our understanding of the growth of the first supermassive black holes, their interactions with quasar host galaxies, and the large-scale structures surrounding them. Additionally, they will collaborate with the Flandrau Science Center & Planetarium at the University of Arizona to develop a "fusion-camp" summer program that will have broad impacts on outreach and education. Theoretical models predict that the earliest billion supermassive black holes (SMBHs) form in massive galaxies and inhabit massive dark matter halos. The PIs will analyze a suite of multi-wavelength datasets collected from ALMA, VLA, and ground-based optical and infrared telescopes for a sample of 25 quasars in the epoch of reionization. These data, combined with data that is being collected from JWST, Chandra, and HST, will enable the team to resolve the long-standing question of whether the earliest SMBHs reside in the most massive dark matter halos and inhabit emerging large-scale galaxy overdensities. This program will also allow them to study the assembly of quasar host galaxies, understand the connection between AGN feedback and early massive galaxy formation, and constrain cosmic reionization and metal enrichment in the early Universe. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.