Stilgar is the head honcho of Sietch Tibr, and he's the Fremen who originally accepts Jessica and Paul into Fremen society.
In many ways, Stilgar is a knight archetype like Gurney. His skills and loyalty cause Paul to refer to him as "[his] right arm" (44.249). He also employs intelligence and cunning on more than one occasion, leading even Jessica to admire him as a "man who weighs his decisions, who thinks of consequences" (32.61).
But unlike Gurney, Stilgar becomes consumed by the religion and mythology surrounding Muad'Dib. Even Paul is saddened by how "Stilgar [has] been transformed from the Fremen naib to a creature of the Lisan al-Gaib, a receptacle for awe and obedience" (48.56). Stilgar changes from a friend and teacher to Paul (like Gurney) to becoming Paul's worshipper, a religious knight who can no longer think for himself.