Adam Smith is most famous for authoring the text "An Inquiry Into The Nature And Causes Of The Wealth Of Nations" (1776), which is more commonly known as "The Wealth of Nations". This text is often cited as the first major work of economics, and the origin of the metaphorical phrase: "The Invisible Hand." It's interesting to note that, even though the invisible hand has become a household phrase in economics, Adam Smith had used the phrase only once in his work.
In his groundbreaking book, Adam Smith argued that free trade, competition and consumer choice would bring about economic growth and a higher standard of living. Similar to how Newton drastically changed how the world understood physics, Adam Smith laid down the foundation and changed how the world understood economics. (Read Adam Smith And "The Wealth Of Nations" to learn more.)