Theodore Roosevelt was President of the United States.
Theodore Roosevelt Jr. ( [ ˈroʊzəvɛlt ] ; October 27 , 1858 -- January 6 , 1919 ) was an American statesman , author , explorer , soldier , naturalist , and reformer who served as the 26th President of the United States from 1901 to 1909 . Following McKinley 's assassination in September 1901 , Roosevelt became president at age 42 , and remains the youngest president . United States presidential election, 1908 . Popular incumbent President Theodore Roosevelt , honoring a promise not to seek a third term , persuaded the Republican Party to nominate William Howard Taft , his close friend and Secretary of War , to become his successor .