This paper presents an observational determination of the bolometric quasar luminosity function (QLF) across redshifts z=0-6, combining measurements from rest-frame optical, soft and hard X-ray, and near- and mid-infrared bands. The study accounts for observed distributions of quasar column densities and variations in spectral energy distribution (SED) shapes, which depend on luminosity. This allows for a reliable integration of observations, providing a baseline in redshift and luminosity larger than any individual survey. The QLF break luminosity and faint-end slope are determined out to z~4.5, with high significance confirmation of a flattening in both the faint- and bright-end slopes with redshift. The best-fit estimates of column density distribution and quasar SED, which depend on luminosity, self-consistently reproduce observed QLFs in all bands and at all redshifts. The study also calculates the expected relic black hole mass function, cosmic X-ray background, and ionization rate as a function of redshift, finding them consistent with existing measurements. The peak in the total quasar luminosity density is well-constrained at z=2.15±0.05. The paper provides fitting functions for the bolometric QLF and its manifestations in various bands, and a script to return the QLF at arbitrary frequency and redshift from these fits. The study highlights the importance of considering luminosity dependence in quasar SEDs and column densities, and shows that the QLF is consistent across different bands and redshifts. The results suggest that the QLF evolves with redshift, with the faint-end slope flattening and the bright-end slope becoming shallower at higher redshifts. The study also discusses the contribution of quasar host galaxy light and its potential impact on observed QLFs, emphasizing the need for careful consideration of host contamination in optical and near-IR surveys. The paper concludes that the bolometric QLF is a robust tool for understanding quasar evolution and the formation of supermassive black holes.This paper presents an observational determination of the bolometric quasar luminosity function (QLF) across redshifts z=0-6, combining measurements from rest-frame optical, soft and hard X-ray, and near- and mid-infrared bands. The study accounts for observed distributions of quasar column densities and variations in spectral energy distribution (SED) shapes, which depend on luminosity. This allows for a reliable integration of observations, providing a baseline in redshift and luminosity larger than any individual survey. The QLF break luminosity and faint-end slope are determined out to z~4.5, with high significance confirmation of a flattening in both the faint- and bright-end slopes with redshift. The best-fit estimates of column density distribution and quasar SED, which depend on luminosity, self-consistently reproduce observed QLFs in all bands and at all redshifts. The study also calculates the expected relic black hole mass function, cosmic X-ray background, and ionization rate as a function of redshift, finding them consistent with existing measurements. The peak in the total quasar luminosity density is well-constrained at z=2.15±0.05. The paper provides fitting functions for the bolometric QLF and its manifestations in various bands, and a script to return the QLF at arbitrary frequency and redshift from these fits. The study highlights the importance of considering luminosity dependence in quasar SEDs and column densities, and shows that the QLF is consistent across different bands and redshifts. The results suggest that the QLF evolves with redshift, with the faint-end slope flattening and the bright-end slope becoming shallower at higher redshifts. The study also discusses the contribution of quasar host galaxy light and its potential impact on observed QLFs, emphasizing the need for careful consideration of host contamination in optical and near-IR surveys. The paper concludes that the bolometric QLF is a robust tool for understanding quasar evolution and the formation of supermassive black holes.