  The Fermi Gamma-ray Space Telescope with its main instrument on-board, the
Large Area Telescope (LAT), opened a new era in the study of high-energy
emission from Active Galactic Nuclei (AGN). When combined with contemporaneous
ground- and space-based observations, Fermi-LAT achieves its full capability to
characterize the jet structure and the emission mechanisms at work in
radio-loud AGN with different black hole mass and accretion rate, from flat
spectrum radio quasars to narrow-line Seyfert 1 (NLSy1) galaxies.
  Here, I discuss important findings regarding the blazar population included
in the third LAT catalog of AGN and the gamma-ray emitting NLSy1. Moreover, the
detection of blazars at redshift beyond three in gamma rays allows us to
constrain the growth and evolution of heavy black holes over cosmic time,
suggesting that the radio-loud phase may be important for a fast black hole
growth in the early Universe. Finally, results on extragalactic objects from
the third catalog of hard LAT sources are presented.
