So, at the beginning of Prelude to Foundation, Hari meets "Chetter Hummin". He goes traipsing around Trantor with him; meeting Dors, going to the library, working for a while, going to mycogen, getting captured at mycogen, going to the slums of trantor and adopting a son, and then finally meeting the daughter of the mayor of Wye.
Only then, after months to years of being on the planet, does he get tipped off that Chetter is Eto Demerzel, the second most powerful man in the galaxy.
Did he never see a picture of Eto? The news back home never had his face in the holobroadcasts? No poster ever displayed his face?