high commission or envoy extraordinary

Catching up on some episodes of Radio 4’s Great Lives series of jured biographies, I found myself being acquainted with quite a lot of heroic, indispensable individuals whom I’ve never heard of before.
I do enjoy the interaction of the champions and expert witnesses—especially when they don’t always choose to celebrate celebrity in the same way—and learning more about the character and background of the famed, but I appreciate even more discovering those overshadowed, interstitial contributors to the course of history, who, like something in between two known quantities that must necessarily be there if just for the sake of preserving the rules of periodicity.
One such essential but presently forgotten individual was statesman and diplomat John Gilbert Winant, US ambassador to the United Kingdom during the crucial years of WWII—introduced by the sitting US legate.  After the progressive Republican served consecutive terms as governor of New Hampshire, overseeing recovery programmes on the state-level that paralleled and complimented national efforts to pull America out of the Great Depression, FDR—recognising talent, crossed party-lines and appointed Winant first to the commission that codified the US Social Security System, c.f., having bipartisan support for Obamacare.
Shortly afterwards, in 1941, FDR named Winant to the UK diplomatic mission—replacing Ambassador Joseph Kennedy, who although a fellow Democrat maintained that US should not become entangled in foreign engagements and did not cut a very inspiring figure during the Blitz. Winant, with his outreach and industrial connections, became instrumental behind the scenes in persuading the US to join the war effort in Europe. Although the campaign on the political front ultimately did secure America’s commitment, some say that FDR dispatched Winant across the Atlantic also in order to avoid a potential challenge to his unprecedented fourth term as president. The BBC discussion includes many anecdotes and analysis that are well worth the listen—a chat that really draws one into the discussion.