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.
Presidency of John Tyler
The presidency of John Tyler began on April 4, 1841, when John Tyler became President of the United States upon the death of President William Henry Harrison, and ended on March 4, 1845. He had been Vice President of the United States for only days when he assumed the presidency. The tenth United States president, he was the first to succeed to the office intra-term without being elected to it. To forestall constitutional uncertainty, Tyler took the presidential oath of office on April 6, moved into the White House, and assumed full presidential powers, a precedent that would govern future extraordinary successions and eventually become codified in the Twenty-fifth Amendment.