The prodigious history of the first SMBHs and their host galaxies: Gargantua and Pantagruel at cosmic dawn

The first SMBHs and their host galaxies represent some of the most extreme astrophysical objects that we currently know at z > 6. Their observed properties allow to constrain possible evolutionary models. Here we present some recent results on the nature of their black hole seeds, on their mass growth rate, and on the assembly history of their host galaxies.