There are two relatively common phrases that often describe the US president: “leader of the free world” and “the most powerful man/office/person in the world.” I think I’ve heard both of those since I can recall (that’d be the early '70s and beyond).
Whether or not those are literally true or measurable, they’ve obviously not described the office forever. I’m not asking if the president is really the most powerful man on earth (we all know who that really is). (And who knows how long they’ll continue to be arguable, for that matter.)
Wikipedia says that “leader of the free world” is a Cold War term, which makes sense, but it doesn’t go into further detail. Does that pre- or post-date the “most powerful man in the world” description?
In other words, when did it become generally accepted that the US president was the most powerful man on earth? Was Thomas Jefferson ever considered the most powerful man in the world? Or Rutherford B. Hayes? How about Theodore Roosevelt?
I believe (correct me if I’m wrong) that Theodore Roosevelt was the first U.S. President to be a player on the international stage and to think of his role as having a major influence outside the borders of the U.S. I don’t know whether the stick he carried was bigger than everyone else’s or not.
All the ones in your last paragraph are WAY too early. The Spanish American War is usually held to mark the US entry as a player onto the world stage, but Europe already regarded Spain as a minor power at that point, and getting their butts kicked by a bunch of upstart renegade colonials didn’t really signify much. The US wasn’t generally ceded position as a “superpower” until after WWII, and before then you couldn’t claim that the US president was more powerful than, say, the PM of Great Britain.
So when did either phrase (“leader of the free world” or “the most powerful man in the world”) become part of common usage? “After the bomb” is a good benchmark (and I did know the ones I named were too early), but when did those phrases turn into unambiguous references to the sitting US president? When did they enter the popular vernacular?
It’s hard to tell precisely from a Google Books search, and Google Books does get really squirelly with dates sometimes, but it appears that FDR was called the LotFW as early as January of 1942. (I’m not sure by whom, but it appears as a quote in a 1944 book).
The earliest instance of “leader of the free world” I’ve been able to find with a cursory Google search is a New York Times article from 1952. I’m sure samclem will be along soon with his mad newspaper-archive-fu, though.