Who is Noah in Turtles All the Way Down?

Noah Pickett is Davis's little brother. He's 13.
Noah and Davis are the sons of billionaire Russell Pickett. He's missing, and there's a $100,000 reward for anyone who finds him. He's a very isolated young boy. Noah barely knew their mother. At one point, Davis says that his father never really took care of them and that he hopes that Russell stays gone. However, Noah tells Aza that he wants his father to come home.
Aza first meets Noah when Davis stops by his house and the girls come inside to wait. Noah is laying on a couch and playing a space combat game on the large television. He's entranced by the game and barely pays attention to Aza or Davis until they leave. The next time she visits, he's playing the same game on the same couch. This time, however, he breaks down and cries to Aza, admitting that he misses his father and can't think straight since he left. He offers to send her some information about his father's disappearance, and Aza wants to keep looking to find Russell for him.
In the end, Noah moves to Colorado with Davis.