I'm gonna take a wild stab at this and say Professor Gast.

He's always mentioned as the most brilliant scientific mind in the world before his death. We know he was killed by Hojo, a man of immense ego, but only after he gave up his studies of the Cetra to marry Ifalna and father Aeris. Of course, we only know all this after Cloud "sees" the video research of all these events after Aeris' death.