Who is Namri from Children of Dune and what is their importance?

Namri is Javid's father, and the Fremen who captures Leto Atreides II when he fakes his own death. He calls himself "Mirzabah" - the "Iron Hammer" - who in Fremen mythology smashes souls that cannot answer satisfactorily on their way to paradise. Leto sees Namri, who is to be his new schoolmaster, as a "human gob jabbar".