George Washington
At the end of his second term, Washington retired for personal and political reasons, fatigued and disgusted with personal attacks, and to assure a truly contested presidential election could be held. He did not feel bound to a two-term limit, but his retirement ultimately set precedent. The two-term limit to the presidency was formalized with the 1951 adoption of the Twenty-second Amendment to the United States Constitution. Washington is often credited with setting the principal of a two-term presidency, but it was Thomas Jefferson who first refused to run for a third term on political grounds.
President of the Continental Congress
The length of a presidential term was ultimately codified by Article Nine of the Articles of Confederation, which authorized Congress "to appoint one of their number to preside; provided that no person be allowed to serve in the office of president more than one year in any term of three years". When the Articles went into effect in March 1781, however, the Continental Congress did not hold an election for a new president under the new constitution. Instead, Samuel Huntington continued serving a term that had already exceeded the new Term limit. The first president to serve the specified one-year term was John Hanson (November 5, 1781 to November 4, 1782).