Franklin, the only president ever to do so, and a central figure in world events during the mid-20th century, leading the United States during a time of worldwide economic depression and total war. A dominate leader of the Democratic Party and the only American president elected to more than two terms, he built a New Deal Coalition that realigned American politics after 1932, as his domestic policies defined American liberalism for the middle third of the 20th century.
His single greatest accomplishment was nothing that can be measured by an analysis of his policies. What FDR did was restoring American confidence and creates sense of optimism in the midst of the Depression. He always sounded hopeful that things would get better and did his best to try and explain what he was doing to try and fix the problem through his fire-side chats over the radio. In doing this, many in America had great confidence in FDR and were highly supportive of him, which is partially why he remains one of the most popular presidents in American history.
In terms of policy success, his real accomplishment was providing regulations for what business could do. The Great Depression was the result of several factors, including bad credit and greed on the part of banks. When the stock-market crashed in 1929, the financial policies that came out of the seeming blooming of the 20s were proved to be faulty, and FDR made sure that their mistakes could not be