David Ricardo (1772-1823) was an English political economist, often credited with systematizing economics, and was one of the most influential of the classical economists. He was also a member of Parliament, businessman, financier and speculator. Perhaps his most important contribution was the theory of comparative advantage. He became interested in economics after reading Adam Smith's The Wealth of Nations in 1799. Ricardo's work with the stock exchange made him quite wealthy, which allowed him to retire from business in 1814. He is responsible for developing theories of rent, wages, and profits. Another idea associated with Ricardo is Ricardian equivalence. He was also an opponent of protectionism for national economies, especially for agriculture. He believed that the British "Corn Laws"-tariffs on agriculture products-ensured that less-productive domestic land would be harvested and rents would be driven up. His works include: The High Price of Bullion (1810) and On the Principles of Political Economy and Taxation (1817).