  We investigate the hypothesis that quasars formed together with the stellar
populations of early-type galaxies. This hypothesis, in conjunction with the
stellar ages of early-type galaxies from population synthesis models, the
relation of black hole mass to bulge velocity dispersion, and the velocity
dispersion distribution from the Sloan Digital Sky Survey, completely
determines the cosmic accretion hystory of supermassive black holes and the
redshift evolution of the characteristic luminosity. On the other hand the
precise shape of the luminosity function of quasars depends on the light curve
of quasars and, in the optical, but not so much in X-rays, on the covering
factor of the dust surrounding the AGN. We find a plausible set of assumptions
for which the coeval formation of supermassive black holes and elliptical
galaxies is in good agreement with the observed B-band and X-ray luminosity
functions of quasars.
