Socrates, according to Plato: To fear death is to think one knows what one does not

To fear death, gentlemen, is no other than to think oneself wise when one is not, to think one knows what one does not know. No one knows whether death may not be the greatest blessing for a man, men fear it as if they knew that it is the greatest of evils. And surely it is the most blameworthy ignorance to believe that one knows what one does not know.

       --Socrates (469-399 B.C.), quoted by Plato in the Apology, translated by G.M.A. Grube. From Plato, Complete Works (1997)