  Active Galactic Nuclei (AGN) unification, which implies a large number of
obscured AGN, can explain the optical, infrared and X-ray content of deep
multiwavelength surveys. Here, we show that the same model also successfully
explains the spectral shape and intensity of the X-ray background. The simplest
possible unified model assumes a constant ratio of obscured to unobscured AGN,
independent of redshift or luminosity. With almost no free parameters, the
predicted X-ray background agrees remarkably well with observations. Both the
observed properties of deep AGN samples and the X-ray background can be
explained by the same model without invoking different evolution for obscured
and unobscured AGN. Recent observational evidence shows that the ratio of
obscured to unobscured AGN may depend on luminosity. An AGN unification model
that allows for such a dependence also fits the X-ray background spectrum, and
the predicted numbers counts in the 2-10 keV X-ray band are in good agreement
with observations. We present predictions for the source counts in hard X-rays
(10-100 keV), which indicate that future missions like the Black Hole Finder
will observe thousands of heavily obscured AGN.
