The most massive BHs finished their growth at z=2; the least massive
ones are still growing today. Following the most massive BHs backward
in time we have recently discovered that such objects started their
growth as relatively small seed BHs at z=10-20 and grew continuously
until about z=4.8. The subsequent evolution is different with short
episodes of fast growth until about z=2.
I will describe the large project that lead to these conclusions and
the consequences to the parallel evolution of galaxies and their
central BHs.