In my searches I kept finding references to Adenet Le Roy, the minstrel, for example from Encyclopaedia Britannica:http://www.uv.es/britan/micro/micro_5_33.html
He was called "King of the Minstrels" because he was the chief minstrel of his patron and presumably ruled over the other minstrels and got them all to play in tune and in tempo with each other.
I don't think there was one patriarch for the LeRoy surname, since there are many various haplotypes. I think it was a common expression what is now Belgium, then Flanders, Hainault, Brabant etc., meaning "chief man of ..." or "master of ..."
From surname distribution maps, LeRoy is more common that either Roi, LeRoi or Roy and is most numerous in Walloon Belgium and in particular the county of Hainault as well as the French Départment Nord which lies just across the Border. As a result of Louis 14th wars he annexed much of Hainault to France.
The following is my theories, so take it all with some grains of salt. Although "LeRoy" is French, meaning "The King", it did not catch on in France itself, where the authority of the King was a real presence. Calling yourself "The King" might get yourself into deep trouble. It could be interpreted as being an insult or a mock of the real king.
The surname LeRoy could only survive in a peripheral area where the authority of the French King was in doubt as it was in Hainault, which was ruled in succession by the Dukes of Burgundy, the Spanish and then Austria.
The off-shoots of LeRoy show a typical Huguenot distribution pattern. In circa 1575, the Spanish Duke of Alva besieged the rebellious cities of the Spanish Netherlands and ultimately forced them to reconvert to Catholicism. They were given one year to accept Catholicism or to leave.
Most accepted, but a large fraction called "Walloons" immigrated to France as LeRoy, Roi, LeRoi or Roy settling in Normandy, Britanny, Alsace and the Huguenot cities in the Loire valley and western sea coast. France at the time was divided between Huguenot cities and strongholds and those that were Catholic.
Others fled to England as LeRoy, Roy and King chiefly to the seaports of East London and Southampton. Some went to the Netherlands as as de Rooij, van Rooij and Rooij. Others went to Germany as Rauhé, Raué, Rohé and Rohe.
One must also factor in a second wave of Huguenot emigration from France circa 1690, when Louis 14th outlawed the Huguenot religion in France.