Who is Moneo Atreides from God Emperor of Dune and what is their importance?

The 118-year-old majordomo and chief aide to the God Emperor Leto II, Moneo normally wears a white Atreides uniform without insignia. He is nearly as recognizable as Leto, with a flat, even face, thick sandy hair, and deep gray eyes that show he understands his personal power. He spends most of his time in a modest office at a cluttered desk, and probably uses an illegal Ixian computer. He is detail-oriented and frustrated when not allowed sufficient time to arrange everything.