Apostolic King was a hereditary title

Title

A title is a prefix or suffix added to someone's name to signify either veneration, an official position or a professional or academic qualification. In some languages, titles may even be inserted between a first and last name...

 borne by the King of Hungary

King of Hungary

The King of Hungary was the head of state of the Kingdom of Hungary from 1000 to 1918.The style of title "Apostolic King" was confirmed by Pope Clement XIII in 1758 and used afterwards by all the Kings of Hungary, so after this date the kings are referred to as "Apostolic King of...

. Saint Stephen (ca. 997–1038) was supposed to have received it from Pope Sylvester II. The king's efforts to Christianize his people led to his comparison to one of the apostles. It was first used by the Holy Roman Emperor

Holy Roman Emperor

The Holy Roman Emperor is a term used by historians to denote a medieval ruler who, as German King, had also received the title of "Emperor of the Romans" from the Pope...

 Leopold I

Leopold I, Holy Roman Emperor

| style="float:right;" | Leopold I was a Holy Roman Emperor, King of Hungary and King of Bohemia. A member of the Habsburg family, he was the second son of Emperor Ferdinand III and his first wife, Maria Anna of Spain. His maternal grandparents were Philip III of Spain and Margaret of Austria...

 (1657–1705) as King of Hungary. The title was last used in the reign of Charles IV (1916–18).

The title is comparable to Spain

Spain

Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...

's Catholic

Catholic Monarchs

The Catholic Monarchs is the collective title used in history for Queen Isabella I of Castile and King Ferdinand II of Aragon. They were both from the House of Trastámara and were second cousins, being both descended from John I of Castile; they were given a papal dispensation to deal with...

 and France

France

The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

's Most Christian King but is of a higher order.