The Fremen inhabit Arrakis, also known as Dune, the desert planet that is the sole source of the spice melange in the known universe. The Fremen came to Dune thousands of years earlier as the Zensunni Wanderers, a religious sect in retreat. Over time, surviving the incredibly harsh conditions of Dune bred them into the ultimate example of humans in extremis: a people bred purely to survive. They took to calling themselves the Free Men of Dune, which was later shortened to Fremen; in an early, alternate Dune outline Frank Herbert called Spice Planet, the Fremen were literally the "Free Men" — convicts who had been transported to "Duneworld" to work for the spice operation of the "Hoskanners" in exchange for a reduction in their sentence.
Each sietch has a Sayyadina, a wise woman trained in the spiritual traditions of her people who frequently functions as an acolyte to a Fremen Reverend Mother, comparable to a Bene Gesserit Reverend Mother. A Sayyadina can also function as a spiritual leader in her own right. There are hints in the novels that the Sayyadina rite preceded the adoption of the role and title of the Bene Gesserit equivalent.
In Dune, Herbert writes that "Paul recalled the stories of the Fremen — that their children fought as ferociously as the adults." Padishah Emperor Shaddam Corrino IV later notes, "I only sent in five troop carriers with a light attack force to pick up prisoners for questioning. We barely got away with three prisoners and one carrier. Mind you, Baron, my Sardaukar were almost overwhelmed by a force composed mostly of women, children, and old men."
Due to the invention of the personal body shield, hand to hand combat has re-entered human conflict; all forms of projectile weapons have been made semi-obsolete. Energy weapons — lasguns — react violently with a shield, creating an explosion comparable to sub-atomic fusion, killing operator and shield wearer. Body shielding may be compromised, but only by moving an edged weapon at a speed slow enough to penetrate the tuning of a shield. Additionally, shields are known to drive the fiercely territorial sandworms of Arrakis into a killing frenzy. For this reason, shields are not used on Arrakis's open regions with any frequency. Consequently, Fremen have an edge in hand to hand combat because they do not slow their weapons when attacking, unlike those used to attacking a shielded enemy. Fremen use different archaic weapons to great effect (firearms, crossbows), but the most deadly and prized possession of a Fremen warrior is the crysknife — a personally tuned blade ground from the tooth of a sandworm. An untreated crysknife will disintegrate soon upon the death of its owner unless it is close to human flesh. Fremen tradition also demands that a drawn crysknife must not be sheathed until it draws blood. In Dune, Paul Atreides (in his role as Muad'Dib) personally trains a force of Fremen "death commandos" (known as Fedaykin) in the use of the Weirding Way.
These rings are used as a form of currency, and are backed by fixed volumes of water (analogous to the historical gold standard). Water rings have a profound significance in matters of birth, death, and courtship ritual.
The special fabric is a micro-sandwich designed to dissipate heat and filter wastes while reclaiming moisture. The water is then held in catchpockets and made available to drink through a tube.
A Fremen in a well-kept suit can survive weeks in the desert without any other source of water.
Because of their culture's focus on water conservation, it is generally considered a great sign of respect (though often interpreted otherwise) for a Fremen to spit before a person.
Fremen, because of their conservation routine, also put a great cultural reverence on crying and tears. Tears shed for someone who has died are referred to as "Giving Water for The Dead."
The Fremen have ofttimes been mentioned in the Dune series of games, playing a vital role in the plots of nearly all of them. The first Dune game and Frank Herbert's Dune are tied closely to the original book by Frank Herbert, retelling Paul Muad'Dib's rise to becoming the Fremen's Messiah, and leading them against the Harkonnens and the Padishah Emperor under the Atreides banner.
In Dune II, the Fremen were special Atreides units, native elite guerillas invoked from the Palace, uncontrollable by the player. The same goes for Dune 2000, though with the minor exception that the Fremen warriors are player-controllable units. There was also a scene where the Fremen naib (which is uncommon, considering the naib was a woman) apparently held the Atreides Mentat at knife-point, supposedly as a threat.
During the War of Assassins in Emperor: Battle for Dune, the Fremen-Atreides alliances forged in ages past has sundered, and the Duke Achillus desperately wants to reestablish it in order for the Atreides supremacy over Dune to succeed. Mentat Kolinnar Koltrass requires the player to help do so by doing the Fremen favours in various parts on Arrakis.
The refusal of the Fremen alliance with the Atreides was featured in the second Atreides campaign cutscene, in which the two Fremen in the screenshot argued over the importance of said alliance. The naib was unwilling to discuss an alliance with the House because "our fathers spilt their water for them" for nothing. Even so, the Harkonnen will overrun the Fremen, while the latter will "stand as Fremen, and fall as Fremen".
Later, shortly after the Sardaukar assassination attempt, the Fremen troop mentioned in the previous cutscene were ambushed by a Harkonnen armor battalion. All hope seemed lost for the troop, when a fleet of ornithopthers flew out of the sky, assaulting the battalion, allowing the Fremen to charge in and mop up the remaining tanks. A while later, the Naib barged into the camp where the Mentat was talking to the player about the said deed, demanding the bodies of his fallen men since "that water belongs my tribe" and he shall have it back, lest he wants the Mentat to "taste my blade". A later explanation later revealed that the bodies of the fallen men were wrapped in microfoil to "preserve their water, they can be returned to you whenever you like". The Naib spat on the floor as a sign of respect to the Atreides commander.
Moments later, a Fremen-Atreides alliance conference was to be held on Caladan, much to the Naib's dismay. A Bene Tleilax assault force of Face Dancers besieged the party, with the Fremen representatives and the Duke later rescued by the player. In return of the player's aid to the Fremen, the massive water-debt owed by the Naib's tribe states that they'll send as many warriors into battle, along with their warrior elite, the Fedaykin.
Being a neutral faction, the Fremen can also choose to be allied with the House Ordos or be destroyed. An alliance with House Harkonnen — though it can be done in skirmishes — in the campaign though, is nearly impossible. In an opening cutscene, a Harkonnen soldier was seen slitting a Fremen warrior's throat, then proceeding to send the corpse rolling down the dunes. At some point in the game though, the Fremen will ally with the Harkonnen if the player plays for that House.
Aside from the typical Fremen warrior, the Fremen Fedaykin Warrior is a relatively new addition to the pantheon of units in the Dune series of games. Utilizing a Weirding Module as their main weapon, their attack is the infantry equivalent of the Atreides Sonic Tank. The Fedaykin are also accomplished Sandriders, luring sandworms using thumpers then proceeding to ride them for a limited amount of time.