George Steiner

The most stringent test of the aliveness of an imagined character—of its mysterious acquisition of a life of its own outside the book or play in which it has been created and far exceeding the mortality of its creator—is whether or not it can grow with time and preserve its coherent individuality in an altered setting. Place Odysseus in Dante’s Inferno or in Joyce’s Dublin and he is Odysseus still, though barnacled from his long voyage through those imaginings and remembrances of civilization which we call myths. How a writer imparts this germ of life to his personages is a mystery; but it is clear that Vronsky and Levin possess it. They live with the times and beyond them.

— Tolstoy or Doestoevsky