Who is Raych Seldon from Forward the Foundation and what is their importance?

Raych Seldonis a tough 12-year-old street urchin whom Hari Seldon and Dors Venabili encounter by accident in the wretched slums of Billibotton "Dahl Sector" during Prelude to Foundation, Raych has an ingratiating quality that convince Hari and Dors to adopted him. It also helps them survive a coup hatched in Wye Sector. Eight years later, as Forward the Foundation begins, Raych is a young adult, proudly wearing the thick, dark mustache of Dahl males and serving as Hari's bodyguard.