Who is Jason Marcus from The Age of Wire and String and what is their importance?

Jason Marcus, also called Jase, is the author's brother. This fact emerges only gradually and obliquely through the course of the book. It also slowly becomes apparent that something happened to Jason. The initial clue given is that Jason is no longer present. Toward the end of the book, the author states that Jason died, although he gives no information about how or when this happened.