  Massive black holes are fundamental constituents of our cosmos, from the Big
Bang to today. Understanding their formation from cosmic dawn, their growth,
and the emergence of the first, rare quasars in the early Universe remains one
of our greatest theoretical and observational challenges. Hydrodynamic
cosmological simulations self-consistently combine the processes of structure
formation at cosmological scales with the physics of smaller, galaxy scales.
They capture our most realistic understanding of massive black holes and their
connection to galaxy formation and have become the primary avenue for
theoretical research in this field. The space-based gravitational wave
interferometer, LISA, will open up new investigations into the dynamical
processes involving massive black holes. Multi-messenger astrophysics brings
new exciting prospects for tracing the origin, growth and merger history of
massive black holes across cosmic ages.
