Teddy Roosevelt served almost two terms as president. He became president after William McKinley was assassinated on Sept. 14, 1901, six months into his term as president.
At the time of the assassination, Roosevelt was only 42 years old, making him the youngest person to ever be president. Because the assassination occurred so early in McKinley's term, Roosevelt served almost an entire first term. He was re-elected in 1904, but decided not to run for another term in the 1908 election. He decided to run for president again in 1912 for the Progressive Party, which was nicknamed the Bull Moose Party. He lost this election to Woodrow Wilson.