Who is Yugo Amaryl from Forward the Foundation and what is their importance?

Yugo Amaryl is a native of the Dahl Sector of Trantor, Yugo is a brilliant self-taught mathematician languishing as a heatsink worker when Hari Seldon and Dors Venabili encounter him in Prelude to Foundation. Hari brings Yugo to the university, sees to his education, and brings him into the psychohistory project as his assistant and planned successor.