I think I am going to attempt to compile a list of those saints that were monarchs of their countries
Bl. Karl I of Austria
St. Louis of France
St. Edward the Confessor
Byzantine (Catholic and Orthodox)
Great King, St. Constantine
Great King, St. Voldomyr and his mother Olha of Kyiv
Bl. Constantine XI
St. Nicholas, last Tsar and Passion-bearer
Protestant Churches (Anglican)
Charles I Stuart, King of England, Scotland, France, etc.
More to come, the list will be updated each time I think of more.If ye know any (like Armenians, Ethiopians, etc) that I missed then leaving a comment would be great. Plus there are many kyivan princes in the Ukrainian calender that I have missed that will require some time to go through and get them all. A fact I always find interesting is that St. Nicholas of Russia and Bl. Karl of Austria were both the last two sovereigns of empires that claimed succession from the Roman Empire, and both fought on opposing sides in WWI.