What is Franklin Delano Roosevelt's famous contribution to America?

Franklin Delano Roosevelt transformed America from a country on its knees into a superpower.

During the Great Depression, President Roosevelt greatly expanded the role of the federal government with his New Deal. Some historians separate the New Deal into two parts, with the second part as more liberal. In the first part there were attempts to deal with the banking crises through the Emergency Banking Act and the 1933 Banking Act, measures meant to keep banks from closing as they did after the stock market crash. To do this, President Roosevelt permitted the Federal Reserve Banks to issue more currency so that emergency calls by banks could be met.
After these banking acts, faith was restored and Americans returned to their banks with the money they had hidden at home. Later, Roosevelt expanded the Banking Act to include the Federal Deposit Insurance Corporation. This FDIC insures individuals' deposits up to US$250,000 in any of its membership banks.

In the second part of the New Deal, expansive social programs such as the WPA (Works Progress Administration) employed thousands of men in huge projects such as the Tennessee Valley Authority, the Hoover Dam, and the many other projects like the Public Works of Art Project which employed artists to enhance public buildings. Earlier there was a project to employ men in building bridges and buildings that was named the Civil Works Administration. However, this program met with much criticism because of its cost and effectiveness, so it was ended and replaced with the WPA. 
Among additional programs in this Second New Deal are the following:

• Farm Security Administration


• National Labor Relations


• Rural Electrification Act


• Social Security


• U.S. Housing Authority

Above all else, President Roosevelt inspired confidence and faith in the American people. After the bombing of Pearl Harbor, he unified Americans with his strength of purpose. He worked with the military, and sometimes around them, to develop strategies for the defeat of Japan and Germany through a series of invasion, beginning with North Africa in 1942 and ending with the D-Day invasion which General Eisenhower executed successfully in 1944. Throughout this time, FDR's fireside chats comforted and encouraged many Americans.

Along with the social programs and the military-industrial complex of the war, FDR brought America out of a depression and, after the victory of the Allied Powers, the U.S. became a superpower that was able to make its influence felt around the world.