COSMIC BACKGROUNDS EMISSION FROM THE ENTIRE EXTRAGALACTIC SKY ACROSS THE ELECTROMAGNETIC SPECTRUM ARE IMPRINTED WITH SOME OF THE MOST IMPORTANT PROCESSES OF THE EVOLUTION OF THE UNIVERSE. AS THE LEFTOVER RADIATION OF THE BIG BANG THE COSMIC MICROWAVE BACKGROUND (CMB) REVEALS THE CONDITIONS IN THE EARLY UNIVERSE AND ITS UCTUATIONS ENCODE THE SEEDS OF LARGE-SCALE STRUCTURE. THE BARYONS IN THESE STRUCTURES COLLAPSE INTO GALAXIES WHERE STARS AND EVENTUALLY BLACK HOLES FORM AND EVOLVE PRODUCING THE BACKGROUNDS AT ALL OTHER WAVELENGTHS (FIGURE 1). AT X-RAY ENERGIES THE BACKGROUND IS DOMINATED BY THE ACCRETION OF GAS ONTO SUPERMASSIVE BLACK HOLES (SMBHS) WHICH POWER ACTIVE GALACTIC NUCLEI (AGN) . THE COSMIC X-RAY BACKGROUND (CXB) ENCOMPASSES THE ACCRETION HISTORY ONTO AND GROWTH OF SMBHS OVER THE HISTORY OF THE UNIVERSE. INTIMATELY TIED TO THEIR HOST GALAXIES AGN ARE FED BY THE SAME PROCESSES THAT TRIGGER STAR FORMATION AND AGN ACTIVITY APPEARS E CIENT AT REGULATING IT IN TURN. ANY MODEL OF SMBH GROWTH AND THE CO-EVOLUTION OF THEIR HOST GALAXIES MUST BE ABLE TO REPRODUCE THE CXB.