Who was the first President of the United States?

George Washington was the first President of the United States, serving from April 30, 1789, to March 4, 1797. As a pivotal figure in the founding of the nation, he played a crucial role during the American Revolutionary War and was unanimously elected as the country's first leader. Washington's presidency set numerous precedents that shaped the role of the executive branch, including the establishment of a cabinet and the two-term limit, which later became a constitutional amendment. His leadership helped to define the office and solidify the principles of American democracy.

The other individuals mentioned had significant roles in American history but were not the first president. Thomas Jefferson, who succeeded John Adams, was the third president and is also notable for drafting the Declaration of Independence. Abraham Lincoln served as the 16th president, leading the nation through the Civil War and working to end slavery. John Adams was the second president and a key figure in the American Revolution, but he followed Washington in the presidency. Therefore, Washington's unique distinction as the first president is why he is the correct answer.