Those who drink the spice mixed with the water which gave them special attributes. Much about the story is not remembered; it’s been years and a life time, after all.
The Bene Gesserit were part of a centuries long selective breeding program designed to direct the course of galactic history through marriages into the ruling families with the ultimate aim of the birth of a male Bene Gesserit who would be able to see through time and space. The book was heavy with religious metaphors.Anyway, Ivanka in that picture looks like my image of one of them. Extremely beautiful, intelligent, eerily composed, and dangerous when confronted with falsehood.