What gave the US the power it's now throwing away was an array of successes that made the US an example of good governance for the entire world: New Deal, Bretton Woods agreeement, victory in WW2, Marshall Plan and NATO. There wasn't a single person in charge of that all, but I think 3 stand out:

* Henry Morgenthau Jr.: secretary of Treasury during Roosevelt, one of the main designers of the New Deal, of financing the US war machine during WW2, and also one of the US negotiators at the Bretton Woods conference

* George C. Marshall: chief of staff of the US Army, organized the victory in WW2, came up with the eponymous plan and carried it forward politically. secretary of State after the War

* Dean Acheson: main designer of the Marshall Plan and of NATO, and one of the US negotiators at the Bretton Woods conference. secretary of State after Marshall

I wouldn't put it on one person, it was basically everyone between Roosevelt and Obama. Not that any of them were exactly geniuses, but we've gone from mostly sober drivers to someone blowing a 0.5 BAC.

JQ Adams, Elihu Root, George Kennan, and Henry Kissinger.

Joe Biden.