Theodore Roosevelt was a leader.
Theodore Roosevelt . He also served as the 25th Vice President of the United States and as the 33rd Governor of New York . As a leader of the Republican Party during this time , he became a driving force for the Progressive Era in the United States in the early 20th century . United States presidential election, 1904 . Incumbent President and Republican candidate Theodore Roosevelt , having succeeded to the presidency upon the assassination of William McKinley in September 1901 , was elected to a term in his own right .