Forty Years of X-Raying Narrow-Line Seyfert 1 Galaxies

Forty years after the discovery of Narrow-Line Seyfert 1 Galaxies (NLS1s), and 20 years since the discovery of the remarkable ultrasoft soft X-ray emissions of NLS1s, strategic publications improved the understanding of the Seyfert phenomenon more generally. New theoretical models emerged from the observations and stimulated the discussions on the innermost regions of AGN. NLS1s are an amazing class of AGN for X-ray, optical and multiwavelength science