8. Thomas Jefferson
Thomas Jefferson was in France when the Constitutional Convention was held, and had little input to the document beyond correspondence with fellow founders during the ratification process. His greatest influence on American history was in his expansion of presidential powers beyond those specified in the Constitution through the purchase of Louisiana. His act more than doubled the size of the United States, ensured eventual expansion to the Pacific ocean, and obtained the port of New Orleans, creating new markets for the farmers and eventual manufacturers within the emerging American west.