What major accomplishment is Thomas Jefferson known for?

Thomas Jefferson is best known for being the principal author of The Declaration of Independence, a foundational document in American history that established the thirteen colonies' intent to separate from British rule. This declaration, adopted on July 4, 1776, articulates the colonists' right to self-governance and outlines the principles of individual liberty and equality. It has had a profound impact not only on the United States but also on democracies around the world.

The other choices reflect significant figures and events in American history but do not accurately represent Jefferson's primary contribution. The first U.S. President was George Washington, not Jefferson. Jefferson did not lead the Continental Army; that role was filled by Washington. While he was a prominent figure in the early United States, he was not a writer of The Federalist Papers, which were penned primarily by Alexander Hamilton, James Madison, and John Jay as a way to advocate for the ratification of the U.S. Constitution.