Who is Paul-Muad'Dib Atreides from God Emperor of Dune and what is their importance?

The God Emperor Leto II's father, Paul-Muad'Dib usurps the Imperial Throne in the original Dune and inspires a violent jihad across the universe. Leto's Golden Path is a reaction to that jihad, and attempt to control humankind and prevent its extinction. Paul-Muad'Dib is one of the myriad of voices that live inside Leto, and he uses his voice when he needs to calm and control the ghola Duncan Idaho, Paul-Muad'Dib's Swordmaster and boyhood teacher. Paul-Muad'Dib sees the solution Leto adopts but shrinks back from the horror of a 4,000-year life as a symbiote.