Thank-you to Selwyn for this information.The Danish royal family is among the oldest in the world; its lineage can be traced back to Gorm the Old in the late 9th century. The early Danish kings expanded their kingdom into parts of Sweden and Norway, and in the 11th century Canute the Great ruled over both Denmark and England.
In 1387 Queen Margrethe ascended the throne and succeeded in uniting Denmark, Sweden, Norway, Iceland, Greenland, and parts of Finland in the Union of Kalmar. Sweden and Finland seceded in 1523 but the rest of the union remained until the early 19th century.
Before 1660 the monarchy of Denmark was elected, meaning the king's oldest son did not necessarily inherit the throne. However, after 1660 the monarchy became absolute, and from this time the king's oldest son always took the throne after his father. In 1849 Denmark received a democratic constitution, which changed the monarchy from absolute to constitutional. This meant the king could not act with legislative or political power. However the monarch is still the ceremonial leader of both church and state, and no law can be activated nor can any translation of the bible within the Folkekirke (the Evangelical Lutheran Church in Denmark) be authorized without the king or queen's signature.