Thomas Jefferson was the principal author of the Declaration of Independence.
Jefferson drafted the document in June 1776 while serving on the Committee of Five appointed by the Second Continental Congress. Congress then debated, edited, and approved the text before adopting it on July 4, 1776.
The other committee members were John Adams, Benjamin Franklin, Roger Sherman, and Robert Livingston. Although Jefferson wrote the initial draft, the final Declaration was a collective congressional document rather than a text published exactly as he first composed it.
Jefferson later became the third president of the United States, serving from 1801 to 1809. A common mix-up is to credit the entire Declaration solely to Jefferson; his principal authorship is distinct from Congress's role in revising and adopting it.