  It is widely agreed upon that AGN and Quasars are driven by gas accretion
onto a supermassive black hole. The origin of the latter however still remains
an open question. In this work we present the results of an extremely simple
cosmological model combined with an evolutionary scenario in which both the
formation of the black hole as well as the gas accretion onto it are triggered
by major mergers of gas-rich galaxies. Despite its very generous approximations
our model reproduces the quasar density evolution in remarkable agreement with
observations.
