Here's a brief overview of Lord Sunday's character and his role in the series:
* Lord Sunday is a powerful and ancient being who has been trapped in the Old Kingdom for centuries. He desires to be free and intends to use the power of the Keys to escape and unleash chaos upon the world.
* He is the main antagonist in the first book, "Old Kingdom." He manipulates events and uses his influence to try and control Arthur Penhaligon, the main protagonist, to gain access to the Keys.
* He is ultimately defeated by Arthur in "Old Kingdom," but his influence continues to be felt throughout the series.
* He is a complex and ambiguous character. He is a powerful and dangerous force, but he also has a sense of history and responsibility that makes him more than just a villain.
He is not the subject of an individual book in the series. The series follows Arthur Penhaligon as he learns about his lineage and the power of the Keys, ultimately taking his place as the rightful ruler of the Old Kingdom.
The story of Arthur, his family, and the Keys is the overarching plot of the series. While Lord Sunday is a significant antagonist, he is not the central focus of the books.