The accretion paradigm states that most, and perhaps all, AGN are powered by accretion onto a supermassive black hole (see, e.g., Blandford & Rees 1991). Within this model plays the most important role, determining the emission properties, and therefore the appearance, of the central source. Objects with high accretion rate ( 0.1) appear as an ``optical'' quasar (of course, equally bright, if not brighter, in X-rays as well), while low sub-Eddington accretion ( 10-2) produces a weak ``radio'' core with substantially less optical emission. A zero accretion rate produces a ``dead'' quasar - a black hole detectable only through its gravitational influence on the galactic nucleus. For a given level, the black hole mass determines mainly the luminosity scaling.