This paper combines a large set of quasar luminosity function (QLF) measurements from various wavelengths, including optical, soft and hard X-ray, and near- and mid-infrared bands, to determine the bolometric QLF over the redshift range $z = 0 - 6$. By accounting for quasar column densities, spectral energy distribution (SED) shapes, and their luminosity dependence, the authors achieve a reliable integration of the observations. They infer the QLF break luminosity and faint-end slope up to $z \sim 4.5$, confirming previous findings of a flattening in both the faint- and bright-end slopes with increasing redshift. The best-fit estimates of the column density distribution and quasar SED are used to self-consistently reproduce the observed QLFs in all bands and at all redshifts. The authors calculate the expected relic black hole mass function, cosmic X-ray background, and ionization rate, finding consistency with existing measurements. The peak in the total quasar luminosity density is constrained at $z = 2.15 \pm 0.05$. The paper provides fitting functions for the bolometric QLF and its manifestations in different bands, along with a script to calculate the QLF at arbitrary frequency and redshift.This paper combines a large set of quasar luminosity function (QLF) measurements from various wavelengths, including optical, soft and hard X-ray, and near- and mid-infrared bands, to determine the bolometric QLF over the redshift range $z = 0 - 6$. By accounting for quasar column densities, spectral energy distribution (SED) shapes, and their luminosity dependence, the authors achieve a reliable integration of the observations. They infer the QLF break luminosity and faint-end slope up to $z \sim 4.5$, confirming previous findings of a flattening in both the faint- and bright-end slopes with increasing redshift. The best-fit estimates of the column density distribution and quasar SED are used to self-consistently reproduce the observed QLFs in all bands and at all redshifts. The authors calculate the expected relic black hole mass function, cosmic X-ray background, and ionization rate, finding consistency with existing measurements. The peak in the total quasar luminosity density is constrained at $z = 2.15 \pm 0.05$. The paper provides fitting functions for the bolometric QLF and its manifestations in different bands, along with a script to calculate the QLF at arbitrary frequency and redshift.