from Wikipedia
here are theories about who the court cards represent. ... The United States Playing Card Company suggests that in the past, the King of Hearts was Charlemagne, the King of Diamonds was Julius Caesar, the King of Clubs was Alexander the Great, and the King of Spades was the Biblical King David. However the Kings, Queens and Jacks of standard Anglo/American cards today do not represent anyone. They stem from designs produced in Rouen before 1516 and by 1540-67 these Rouen designs show well-executed pictures in the court cards with the typical court costumes of the time. In these early cards the Jack of Spades, Jack of Hearts and the King of Diamonds are shown from the rear, with their heads turned back over the shoulder so that they are seen in profile. However the Rouen cards were so badly copied in England that the current designs are gross distortions of the originals.
Other oddities such as the lack of a moustache on the King of Hearts also have little significance. The King of Hearts did originally have a moustache but it was lost by poor copying of the original design.