Thomas Jefferson was a prominent American leader who was heavily influenced by the Age of Enlightenment. He adopted many Enlightenment ideas that emphasized reason and individualism. Jefferson was the principal author of the Declaration of Independence, which drew from Enlightenment philosophy and expressed ideals of life, liberty, and the pursuit of happiness. Jefferson later played a key role in establishing the democratic foundations of the United States through his work on the Constitution and as the third President. He also made important contributions as an inventor, philosopher, and founder of the University of Virginia.