Who is Carol Doig from This House of Sky: Landscapes of a Western Mind and what is their importance?

Carol Doig is the author's wife, with whom he has successfully spent decades of his life. While she does not have a front-and-center position in the early parts of the book, she was actually present in the author's life during his journey of hosting his father and grandmother, and throughout the entire process of writing the book that this summarizes.