  We make use of the first high--resolution hydrodynamic simulations of
structure formation which self-consistently follows the build up of
supermassive black holes introduced in Di Matteo et al. (2007) to investigate
the relation between black holes (BH), host halo and large--scale environment.
There are well--defined relations between halo and black hole masses and
between the activities of galactic nuclei and halo masses at low redshifts. A
large fraction of black holes forms anti--hierarchically, with a higher ratio
of black hole to halo mass at high than at low redshifts. At $z=1$, we predict
group environments (regions of enhanced local density) to contain the highest
mass and most active (albeit with a large scatter) BHs while the rest of the BH
population to be spread over all densities from groups to filaments and voids.
Density dependencies are more pronounced at high rather than low redshift.
These results are consistent with the idea that gas rich mergers are likely the
main regulator of quasar activity. We find star formation to be a somewhat
stronger and tighter function of local density than BH activity, indicating
some difference in the triggering of the latter versus the former. There exists
a large number of low--mass black holes, growing slowly predominantly through
accretion, which extends all the way into the most underdense regions, i.e. in
voids.
