Isaac Roosevelt (December 19, 1726 – October 1794) was an American merchant and Federalist politician. He served in the New York State Assembly and the state Constitutional Convention and achieved the most political success of any Roosevelt before Theodore Roosevelt. Isaac was the patrilineal great-great-grandfather of President Franklin Delano Roosevelt. He was the second generation of what would later come to be known as the Hyde Park, New York branch of the extended Roosevelt family. Isaac's fortune from the refining of sugar (a crop produced at the time almost entirely by enslaved persons), and his political accomplishments, became an essential root of the substantial wealth, prominence and influence that the Hyde Park Roosevelts came to amass.