Roosevelt, unlike his predecessor Herbert Hoover, took a leading and vocal role in attacking the effects of the Great Depression. Franklin Roosevelt's response to the Great Depression was a massive collection of government programs, administrations, and agencies that attempted to provide relief, bring about recovery, and establish permanent structural reforms. This effort, known as the New Deal, fundamentally and permanently altered the role of the President, and the federal government in general.
While Hoover was not the laissez-faire doctrinaire that many have accused him of being, he did not advocate direct relief, and he was not particularly good at communicating his policies to the American people, which made him seem aloof to their suffering. Roosevelt, on the other hand, implemented immediate relief and "make-work" programs, and directly communicated to the American people through "fireside chats" and through sending representatives, including his wife Eleanor, throughout the country to meet with people and discuss their hardships. So the role of the President as national leader certainly increased in importance under Roosevelt as a result of his reaction to the New Deal. His popularity with the people, in fact, caused him to overstep his bounds on several occasions, particularly his "court-packing" scheme of 1937, when he sought to add additional justices to the Supreme Court, which had just scuttled some of his reforms. This hurt Roosevelt politically, but there is no doubt that his approach to the presidency during the Great Depression--and equally the Second World War--increased the powers and the scope of the federal executive.