The King (also known as Rudolph IX, King of Trenjen, Frinjen, and Corriarden, Protector of Leathe, and Overlord of the Fiveir of the Orthe), is a small unassuming-looking man with glasses and an extremely powerful magical birthright. This clearly enables him to see the truth about those he is observing, and to cloak himself from visibility to everyone except his own royal relatives -- a skill that comes in handy when he decides to go to a market and pick out his own fruit.
So when the King encounters Mrs. Gladys Naismith, from Earth, he is shocked to realize that she can see him. She in turn is rather shocked to realize that the small man with the string bag of oranges is the royal resident of the Palace that a phalanx of guards and a boatload of magical wards are busy keeping her from entering.
After listening to the stories of Gladys and her traveling companion, the King sets in motion some rather sweeping changes to the way business will be done henceforth in both Arth and the Pentarchy, and then sets off with them through the holy groves of the Goddess to right the wrongs that are currently in motion over in Leathe.
He's not a flashy king, but he's every bit the powerful Royal that this story needs to have in charge of his world.