A cure for polio... FDR created many new jobs with the CCC (Civilian Conservation Corps). They built bridges, cut down trees, etc.
He was the 27th president, and he is the only president that held both offices.
It was a fall of the major Pre-Columbian civilization of the time, and probably the only real power in America capable of standing up to the conquistadors. With the fall of Tenochtitlan it could be said that nothing else stood in the way of the European conquest of the Americas.