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.