David Ricardo was a British political economist and stock trader. He was often credited with systematizing economics, and was one of the most influential of the classical economists, along with Thomas Malthus, Adam Smith, and John Stuart Mill. He was also a member of Parliament, businessman, financier and speculator, who amassed a considerable personal fortune. Perhaps his most important contribution was the theory of comparative advantage, a fundamental argument in favour of free trade among countries and of specialisation among individuals. Ricardo argued that there is mutual benefit from trade even if one party is more productive in every possible area than its trading counterpart, as long as each concentrates on the activities where it has a relative productivity advantage.