The King is the fictional Monarch in To Play the King.
Having recently succeeded his mother as monarch, he is determined to play a more active role in government, but Urquhart thwarts the new king's initial attempts. As his and Urquhart's relationship deteriorates, the King starts to raise issues against government policy, causing the government to lose popularity. As Urquhart faces re-election, the King organises a nationwide tour to highlight the issue of homelessness. He is humiliated in a dirty trick, and Urquhart wins re-election, much to the king's displeasure.
After his re-election, Urquhart demands the King's abdication. Although the King cautions Urquhart that he will continue to fight his policies, he does not feature in the later series.
In the novel, it is the king who decides to abdicate, against Urquhart's wishes and plans.
The King appears to be based, judging by similarities in mannerisms, personal views and even voice, on Charles, Prince of Wales, the current heir apparent to the British throne.