George Washington became the first president under the U.S. Constitution, part of the history marked by America250.
Washington was unanimously elected by the Electoral College in 1789 and took the oath of office in New York City on April 30 of that year. He served two four-year terms, from 1789 through 1797, establishing precedents for the new executive office.
Before becoming president, Washington had commanded the Continental Army during the American Revolutionary War and had presided over the Constitutional Convention. Those roles made him a central figure in both independence and the creation of the federal government.
John Adams was the first vice president and became the second president. Thomas Jefferson served as the third president, while James Madison was the fourth, so all three are plausible but incorrect answers to this question.