Who is Harv from The Diamond Age, or, Young Lady's Illustrated Primer and what is their importance?

Harv is the name of Nell's brother in the context of the novel, as well as the name of the Princess' brother in the context of the sub-story told by the Primer. When the novel begins, Harv is about nine years old. He takes great care of his sister and constantly protects her. He brings her gifts and shows her how to use technology.