Final answer:
Thomas Jefferson was the American Founding Father who authored the Declaration of Independence and served as the third President of the United States, significantly shaping the nation through his Enlightenment-influenced ideals and major achievements like the Louisiana Purchase.
Step-by-step explanation:
The American Founding Father and the principal author of the Declaration of Independence, who was also the third President of the United States, is Thomas Jefferson. Born in Virginia in 1743, Jefferson became a significant figure in early American history, not only for his role in drafting the Declaration but also for his leadership as President. As a Virginia planter, he was actively involved in the political proceedings of his time, serving in the House of Burgesses and the Continental Congress, where he had a pivotal role in severing ties with Great Britain.
His presidency saw landmark achievements like the Louisiana Purchase in 1803 and the commissioning of the Lewis and Clark Expedition in 1804. Jefferson's influence was further solidified by his commitment to Enlightenment ideals, like those of John Locke, which espoused individual rights and government by the consent of the governed, as evident in the Declaration of Independence. His legacy is marked by his advocacies for liberty, his presidential accomplishments, and as the founder of the University of Virginia before his death on July 4, 1826, the 50th anniversary of America's independence.