I don’t mean individuals who, by virtue of an office, function as heads of state or government in two countries, such as the British monarch holding the crowns of many Commonwealth realms, or the French president being one of the princes of Andorra. I’m not referring to constellations of mergers (two states merge, and the head of state of one country becomes head of the newly formed country afterwards) or dissolutions (a state breaks up, and the former head of the old state becomes head of one of the two successors), either. What I mean is: Has any individual ever ruled or governed two distinct nations, simultaneosly or successively, by fulfilling the constitutional requirements for being vested with this office, independet of each other?
There are quite a few examples that arose out of marriages between younger members of royal families, where progeny eventually became the heriditary monarch for both thrones. One that pops to mind is King James VI of Scotland, who became King James I of England after Queen Elizabeth I passed away, and thus King James I of the United Kingdom …
James VI. He was king of Scotland by virtue of being the son of Mary, Queen of Scots and also succeeded Elizabeth I as King of England as James I.
ETA - Drat, there weren’t any replies when I started this. ::sniffle::
Henry of Valois. He was elected King of Poland/Lithuania in 1573. Two years later, on the death of his brother, he went home and ruled France as Henry III.
While she didn’t rule, Mary, Queen of Scots, was Queen of France before becoming Queen of Scotland (where she did sort-of rule).
Sorry! You’d have looked more original if I’d gone with my actual first thought, Emperor Charles V of the Holy Roman Empire, but I couldn’t get my thoughts straight on all of the kingdoms & titles he held …
Who was my second thought, but I already had the bit about James typed out when I saw your reply. Let’s say we just chalk it up to great minds and all that. 
Does that count, though? Queen Consort is more like the First Lady than an actual head of state …
(Although, had her husband, King Francois II survived & they had had children, their heir would have ended up as the monarch of France, England, and Scotland. Fun hypotheticals to trace there, let me tell you …)
Sigismund III Vasa was elected king of Poland (and Grand Duke of Lithuania) and later inherited the throne of Sweden.
Could you clarify this? It sounds like this “exception” would rule out anyone who could possibly be the answer to the question.
I’m just throwing out possibilities; it’s up the OP to determine if that counts.
However, Henry III clearly fits the OP. He did rule in two different countries, and there was no union or other connection between the two. He went to rule in Poland because at the time they elected their king, and Henry didn’t expect to have a shot at being King of France.
Well, he wasn’t quite the ruler of two countries, but Sam Houston was head of the independent country of Texas, and also served as governor of Tenessee, and later as governor of Texas. He was also a congressman.
Pu-Yi was the Last Emperor of China (and has two films made about him under that title), and was also the puppet ruler of the Japanese-administered Manchkuo.
I recalled things like this happening in Scandanavia quite a bit, historically; in the process of refreshing my memory, I discovered that Wikipedia has a list as long as your arm of personal unions, the fancy name for the type of arrangement the OP is talking about. However, the list does include the “codified” unions that the OP was less interested in, such as Elizabeth being, say, the Queen of Canada by virtue of holding the office of Queen of England.
Depending on how you consider the way he achieved office, Simon Bolivar could fit the description.
According to the Wikipedia article, the Hapsburg Maximilian was, at different times:
He was also regent in Vienna and a Viceroy.
Augustus III the Strong was simultaneously and separately Elector of Saxony and King of Poland, having inherited Saxony and been elected to the latter office by the Sejm.
William III of England, Scotland, and Ireland (three separate crowns united in one monarchy) was also and separately Stadtholder of the United Provinces (i.e., hereditary head of state and government of the Dutch Republic).
Georges I, II, and III of Great Britain and of Ireland, and Georges III and IV and William IV of the United Kingdom, were also and separately Elector of Hanover. Both titles, though, came hereditarily, but the governments were kept fully distinct.
Napoleon was of course briefly head of state of Elba (I’m not sure what specific title was hung on him) between his two stints as Emperor of the French.
Leopold II, King of Belgium, was also owner of a “corporate state,” the Congo Free State, which he held through owning the company which ran it. This was very carefully kept distinct from his role as the monarch of Belgium – until his mismanagement of it caused the Belgian government to take it over from him as what became the Belgian Congo.
Norton I served simultaneously as Emperor of the United States and Protector of Mexico.
A cheating way to get your answer, but Rt. Hon. Don Stephen Senanayake, was the head of state for both Ceylon and Sri Lanka. OK, OK you said in the OP not to do things similar to this, but I happened to know this because I was on island for the change over, and it confused passport officials for months afterwards.
They would say, “But sir, you don’t have an exit stamp for Ceylon.,”
I would agree, and try to explain, then they would say I had a point, but restated their point that I couldn’t be let into their country until I had officially left Ceylon. That it was no longer in existance didn’t seem to suffice as a reason. I would attempt to point out that I didn’t have an entrance stamp for Sri Lanka either, but they would just say that Sri Lanka’s laxness in keeping track of who entered their country was of no interest to them.
This doesn’t count, because whoever is the head of state of the United Kingdom automatically becomes head of state of Canada, Australia, and assorted riff-raff. So it’s not that Elizabeth wrangled herself a job as queen of the UK, and then weaseled into becoming queen of Canada. There’s one job, queen of the commonwealth, and whoever is queen of the commonwealth is queen of the UK, Canada, and so forth. Otherwise we could say that Betsy is queen of Northern Ireland, Queen of Scotland, and Queen of England, nevermind that they are united into one kingdom. So this isn’t a case of one person holding many posts, it is a case of one post that covers multiple countries.
Well, yes, but for every case like that now, it had to originate somewhere. One of Lizzy’s ancestors who was already monarch of England and other places added “monarch of Canada” to es list of titles. Likewise for Australia, and (Northern) Ireland, and Wales, and Scotland, and all the rest of the Commonwealth.
And I’m not quite certain that “monarch of the Commonwealth” is all one title, either. It’s my understanding that Canada, say, could in principle change the succession rules for the monarchy of Canada, without the approval of any of the other places Lizzy is Queen of. It just so happens that they all currently have the same monarch, and the same succession rules so they’ll keep with the same monarch, but that’s not an essential feature of the arrangement.
I think so too, but it’s disputed. There was a debate about this between Northern Piper and another poster at some point; I’ll try to find it if I can.