Think you know who the first 8 presidents were? You don't. At least I didn't, and I'm a history dork. This is something you don't read about in the history books, but there were eight presidents between the end of the Revolutionary War in 1781 and the adoptation of the Constitution in 1789. They were 1-year presidents under the Articles of Confederation...
John Hanson (1781), Elias Boudinot (1782-83), Thomas Mifflin (1783-84), Richard Henry Lee (1784-85), John Hancock (1785-86), Nathan Gorman (1786-87), Arthur St. Clair (1787-88), and Cyrus Griffin (1788-89).
This fascinating article explains it.
Washington was just the first president under the Constitution.