William Shakespeare - he covered everything and every nuance of the human soul, from love to envy, from sadism to sublime romance.
Feodor Dostoevsky - His novels are even by today standards supreme achievements of crime stories, Gothic atmosphere, incredibly deep plunging into the darkest secrets of the human psyche
Leo Tolstoy - The most towering vision of the society and humans in general, the guy that everybody revered, loved, looked upon to. A real emperor of the literature, a Caesar in all merits
Anton Chekhov - My personal favorite, in the past he used to be my everyday spiritual bread. The most delicate observer while the most merciless with human hope in general. By far the best short story writer of all times and the best play writer of the modern era
Special mentions - Homer, Gustave Flaubert, Victor Hugo, Guy de Maupassant, Stendhal, Thomas Mann, Nikolai Gogol.