The Bene Gesserit are an ancient and secretive sisterhood of women who have developed extraordinary mental and physical abilities through generations of training and selective breeding. Their powers include the Voice (a form of command that compels obedience), Other Memory (access to the genetic memories of female ancestors), and superhuman observation and deduction. For thousands of years, the Bene Gesserit have pursued a covert breeding programme designed to produce the Kwisatz Haderach - a male Bene Gesserit with the ability to see where they cannot. The sisterhood operates as a political power behind every throne in the Imperium, placing their trained sisters as wives, concubines, and advisors to the ruling houses. The Bene Gesserit are neither heroes nor villains - they are pragmatists playing a longer game than anyone else, and their plans span centuries.

The Fremen are the native people of Arrakis - desert-hardened survivors who have adapted to the planet's brutal conditions over generations, developing a culture centred on water conservation, martial prowess, and a deep spiritual connection to the desert and its sandworms. Dismissed by the Imperium as primitive savages, the Fremen are in fact among the most formidable fighters in the known universe - a fact that Paul Atreides recognises and leverages to build an army capable of overthrowing the Emperor. Fremen society is organised around sietches (underground communities), led by Naibs, with a Reverend Mother serving as spiritual guide. Their secret long-term project to terraform Arrakis into a green world, guided by the planetologist Liet-Kynes, is one of the novel's most prescient ecological themes. The Fremen's adoption of Paul as their prophesied Mahdi drives the political and religious transformation of the entire universe.