George Washington was not the first President of the United States. That honor goes to John Hanson who held the office between 1781 and 1782 under the Articles of Confederation. He was one of eight men to serve as President under the Articles before George Washington ever took office. Though he was limited to a term of one year, he accomplished much in that time and established many of the traditions still followed by Presidents today. Should Hanson be considered the Father of the United States instead of Washington? In a word, no.
It is a bit disingenuous to say that John Hanson was the first President of the United States, because he did not serve as President the same way that Washington served. The Articles of Confederation established an extremely weak central government with no executive branch, so he served in a role more similar to that of a prime minister or speaker of the house than he did to what we think of when we think of the office of President. He was not commander-in-chief and his power was severely limited.
Saying that John Hanson was the first President of the United States is, however, partially supported. There were several presidents of the Second Continental Congress and two Presidents of the Continental Congress, but Hanson was different in several ways. He was the first President of the Continental Congress elected after all 13 former colonies had ratified the Articles of Confederation and after the British surrender at Yorktown. He was also the first to serve as President for an entire one-year term in office and the first to formally use the title "President of the United States in Congress Assembled" in diplomatic dealings.
Thus, saying that John Hanson was the first President of the United States is really a matter of perspective. If you use that particular perspective, then other founders such as John Hancock and Richard Henry Lee were Presidents too. Again, that term itself is deceiving because the office of President of the United States in Congress Assembled was vastly different from the office of President created by the Constitution. Even in his own day, Hanson was not considered the first President, so it is curious that some in the modern day try to make that claim.
Unfortunately, there is a great deal of confusion about John Hanson partially because so little is known about him. He was an important figure during the Revolution, but we cannot be sure about many of the details of his life. Because of this, several writers during the 19th century simply made up stories to fill in the gaps in his life. This has led to a number of misconceptions about John Hanson beyond the famous claim that he was the forgotten first President. These include the claims that Hanson was descended from an African slave, that he created our modern Thanksgiving holiday, and that he was Sweedish. None of these claims are supported, yet they continue to circulate.