Who is Stiros from Heretics of Dune and what is their importance?

Stiros is a Rakian priest, Stiros pushes for a scientific study of the young desert girl Sheeana, opposing the High Priest Hadley Tuek, who regards her reverentially as God's Holy Child. Too old to succeed Tuek, Stiros wants one of his sons, grandsons or nephews to inherit the position of High Priest some day. Cynical, Stiros has a final confrontation over theology with old Tuek before leading a failed assassination attempt against Sheeana.