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

Hari Seldon is the protagonist of both Foundation prequels, Prelude to Foundation and Forward the Foundation, Hari Seldon is a mathematician from an obscure outer world, Helicon, who at age 32 travels to the center of the Galactic Universe, Trantor, to deliver a theoretical paper on psychohistory. Hari is adept in both mathematics and the manual arts such as "Twisting" but knows little history until he meets Dors Venabili at Strelling University, who takes him under her wing. In a complex plot, Dors is assigned in the first novel as Hari's protector, accompanying him around the vast planet, avoiding the clutches of the true power behind the Imperial Throne, Eto Demerzel.