Adam Smith
In the Wealth of Nations Adam Smith asks 'what can a person do that is best for his country?' He decides that if every person does what is best for themself and their little circle of family and friends, then the country will do better. This is because every person knows a lot about their own situation (what they need and what they want, what works and what does not work), much more than the government knows. This sort of thinking is called "liberal theory", a main part of liberalism.