Gottfried Wilhelm Leibniz (1646–1716) was a German philosopher, mathematician, physicist, scientist, politician, diplomat, historian and librarian. He is known as the last universal genius and as one of the most famous philosophers of his time. Leibniz invented a mechanical calculator, developed the infinitesimal calculus, anticipated modern computational science and paved the way for the discovery of the principle of the conservation of energy in physics. He was one of the first to solve mechanical problems by self-regulating systems, anticipated modern geology in claiming that the earth has a molten core and paved the way for the distinction between conscious and subconscious states. Leibniz exchanged more than 15 000 letters with both intellectual and political persons of distinction, among them two German emperors, Tsar Peter the Great and almost all important scientists and philosophers of his time.