The Federal Reserve System (also known as the Federal Reserve, and informally as the Fed) is the central banking system of the United States. It was created on December 23, 1913, with the enactment of the Federal Reserve Act, largely in response to a series of financial panics, particularly a severe panic in 1907.
Over time, the roles and responsibilities of the Federal Reserve System have expanded, and its structure has evolved. Events such as the Great Depression in the 1930s & 9/11 in 2001 were major factors leading to changes in the system.
Adapted from Wikipedia