Catherine the Great and Denis Diderot Self-proclaimed adherent of Enlightenment ideals, Russian empress Catherine the Great enthusiastically corresponded with philosophes like Voltaire and Denis Diderot. When Diderot put his library on sale to raise much-needed funds, Catherine sent him the money but allowed him to keep his books. Historians have long debated the “enlightened despotism” represented by Catherine and other absolutist rulers.

Diderot: By Louis Michel van Loo [1707–1771]/Musée du Louvre, Paris, France/Fine Art Images/Heritage Images/Getty Images