[PDF] Autobiography of Theodore Roosevelt By Theodore Roosevelt. Theodore Roosevelt was the twenty-sixth President of the United States. A leader of the Republican Party and of the Progressive Party, he was a Governor of New York and a professional historian, naturalist, explorer, hunter, author, and soldier. He was a Progressive reformer who sought to move the dominant Republican Party into the Progressive camp. He distrusted wealthy businessmen and dissolved forty monopolistic corporations as a "trust buster". He was clear, however, to show he did not disagree with trusts and capitalism in principle but was only against corrupt, illegal practices. Roosevelt was a great personality, a great activist, a great preacher of the moralities, a great controversialist, a great showman. He dominated his era.