  We use highly spectroscopically complete deep and wide-area Chandra surveys
to determine the cosmic evolution of hard X-ray-selected AGNs. We determine
hard X-ray luminosity functions (HXLFs) for all spectral types and for
broad-line AGNs (BLAGNs) alone. At z<1.2, both are well described by pure
luminosity evolution. Thus, all AGNs drop in luminosity by almost an order of
magnitude over this redshift range. We show that this observed drop is due to
AGN downsizing. We directly compare our BLAGN HXLFs with the optical QSO LFs
and find that the optical QSO LFs do not probe faint enough to see the downturn
in the BLAGN HXLFs. We rule out galaxy dilution as a partial explanation for
the observation that BLAGNs dominate the number densities at the higher X-ray
luminosities, while optically-narrow AGNs (FWHM<2000 km/s) dominate at the
lower X-ray luminosities by measuring the nuclear UV/optical properties of the
Chandra sources using the HST ACS GOODS-North data. The UV/optical nuclei of
the optically-narrow AGNs are much weaker than expected if they were similar to
the BLAGNs. We therefore postulate the need for a luminosity dependent unified
model. Alternatively, the BLAGNs and the optically-narrow AGNs could be
intrinsically different source populations. We cover both interpretations by
constructing composite spectral energy distributions--including long-wavelength
data from the MIR to the submillimeter--by spectral type and by X-ray
luminosity. We use these to infer the bolometric corrections (from hard X-ray
luminosities to bolometric luminosities) needed to map the accretion history.
We determine the accreted supermassive black hole mass density for all spectral
types and for BLAGNs alone using the observed evolution of the hard X-ray
energy density production rate and our inferred bolometric corrections.
