While the discovery of quasars in 1963 (Schmidt 1963) is well known 1, I would like to mention that it was preceded in 1958, forty years ago, by a key paper by Burbidge at the Paris Symposium. He pointed out that tremendous energy, 1060 ergs, resided in extragalactic radio sources. This was an unprecedented amount for the time, and the paper was influential in forcing people to think about non-stellar sources of energy in galaxies, that is, what we now call activity in galaxies.
To continue with the topic of milestone years, we can also note that the evolution of the quasar population was discovered by Schmidt in 1968, thirty years ago, a discovery that was an essential first step to showing that the characteristic time-scale for quasar activity is quite short in cosmological terms.
1 The 1st Texas Symposium on Relativistic Astrophysics (Robinson, Schild, & Schucking 1965) still makes excellent reading about that feverish first year of work. Back.