Factions are Stalker clans/organizations operating within the Zone. Each faction has their own ideals and goals, as detailed in the links below. The factions can have both allies who may share their ideals and enemies who oppose them. Factions play a large role in a Stalker's life, as the Zone is an unforgiving wasteland, where the death of an ordinary Stalker is amounts to little more than a discarded shell casing, and "morality" is relative to a factions goals. Joining other people with the same view of the Zone is often an individual's best avenue for survival in the Zone. The list of major factions in the Zone are:
The Ukrainian military supposedly has the Zone contained in order to prevent the looting of dangerous, radioactive materials and to prevent the unauthorized entering of any individuals. They allegedly enforce this rule with a "Shoot-on-sight" declaration. In an ironic twist, because of major corruption within their ranks, they themselves are the reason why Stalkers can continue to operate, and why radioactive materials from the Zone keep flowing to the outside world. Overtly, the Military are hostile to all Stalkers, to keep up appearances; but they also make shady dealings with them at the same time.
In S.T.A.L.K.E.R.: Shadow of Chernobyl, the Military has strong control over most of the Zone, and nearly all are hostile.
In S.T.A.L.K.E.R.: Clear Sky, the faction is not joinable, and almost all are hostile.
In S.T.A.L.K.E.R.: Call of Pripyat, the player is a Military Agent; therefore, other Military faction members range from neutral to friendly to the player.
The Bandits are raiders and marauders of the Zone, ranging from petty thugs and gangsters to organized crime syndicates. Apart from Freedom, which treats them with marginal contempt, everyone hates the Bandits due to their nefarious acts of robbing and exploiting honest Stalkers. Most Bandits are unorganized and leaderless; there are only a few known Bandit leaders and camps, and even then their groups are still fairly disorganized, with underlings always trying to take control by overthrowing the previous leader. Their unit size is mediocre, and their equipment is cheap and shoddy; because of this they've adapted to a guerilla style of warfare, ambushing small groups with large numbers by camping in locations just off the normal paths.
In S.T.A.L.K.E.R.: Shadow of Chernobyl, Bandits are generally hostile. Should the player join Freedom, Bandits and Mercenaries may become neutral, while, conversely, Duty and Scientists become hostile.
In S.T.A.L.K.E.R.: Clear Sky, the Bandits are neutral (excluding the Renegades) and are a joinable faction; however, they will attempt to extort the player whenever possible. They hold a base in the warehouse in Garbage and hold most of the Garbage. They are at war with the Loners.
In S.T.A.L.K.E.R.: Call of Pripyat, the Bandits are once again neutral, to an extent, and the player can earn their favour; however, some groups will still try to extort the player, even if the player is in full favor with the faction in general.
Duty was founded by former military expedition survivors and Stalkers concerned about the looming horrors of the Zone. They are one of the largest Stalker clans in the Zone. They have a strict military code (such as no smoking, maintaining one's weapons, etc...) and operate in a military fashion, using ranks like Sergeant, Major, Captain, and General. Their goal is to contain and destroy the Zone, fearing that it will spread to the outside world. They view the Zone as an ulcer in the world and their efforts are a way to excise it. They do this with blunt force by killing mutants, eliminating all who oppose them or exploit the free, and burning down or drowning mutant dens. They are neutral toward other Zone factions, save for the Bandits and their long-time nemesis: the Freedom faction. It is said that Duty also has deep connections within the military, specifically Spetsnaz detachments within the Zone, although they treat regular grunts with utter contempt.
In S.T.A.L.K.E.R.: Shadow of Chernobyl, they are one of the best-equipped factions. Most are paramilitary, and some ignore the fragile general truce with Freedom, and organize raids against them. Duty and Freedom become actively hostile to each other in the rush towards the center of the Zone. Thus, if the player is in favor with Duty, he can assist Duty against Freedom, making Duty more likely to push the furthest into Pripyat. They hold Rostok, with their main base of operations near the 100 Rads bar and the Arena.
In S.T.A.L.K.E.R.: Call of Pripyat, the faction has made an uneasy truce with Freedom, observing a ceasefire within Yanov Station; however, outside the station they are hostile to each other. If the player aligns with Duty, their numbers will increase, and Nitro will lower his prices for equipment service & upgrades; conversely, Hawaiian will increase his prices.
In S.T.A.L.K.E.R.: Shadow of Chernobyl, they are the second-largest faction in the Zone (the first being Monolith), and have some of the best equipment. They aren't officially at war with Duty at this time, but fights still break out between the factions from time to time. They hold the Military Warehouses as their main base. If the Marked One is in favor with Freedom, then he can assist Freedom against Duty, making Freedom more likely to push furthest into Pripyat. They hold The Barrier in the Army Warehouses, keeping the Monolith faction and Mutants at bay.
In S.T.A.L.K.E.R.: Clear Sky, the faction is still the second-largest, but are actively at war with Duty. They hold the entire Dark Valley, with outposts in several other locations, and during Clear Sky they take over the Army Warehouses and begin to set up a new base.
In S.T.A.L.K.E.R.: Call of Pripyat, Freedom is still the second-largest faction, and remain in conflict with Duty, although a mutual ceasefire is observed between the two at Yanov Station. Freedom and Duty members shoot each other on sight once outside Yanov. If the player lean towards favoring Freedom, this will increase the faction's strength, and Hawaiian will lower his prices for equipment; but conversely Nitro's prices for maintenance and upgrades will increase.
Loners / Free Stalkers / Neutral Stalkers
Loners are a nomadic semi-unified group of Stalkers who simply live off the Zone in order to earn some coin for their daily lives. Loners are neutral toward almost all other factions, but do have complications with the Military, and, to a lesser extent, the Mercenaries, and openly oppose the Bandit faction for their actions against free Stalkers. Most Loners are only concerned with the riches of the Zone, and do not pay attention to the other factions' hatred for each other - provided, of course, they do not threaten them. Because of this, Loners are often recruited by various factions as mercenaries.
In S.T.A.L.K.E.R.: Shadow of Chernobyl, most of the Loners aren't in a faction (hence the name "Loner"); however, some have banded together into small factions, most notably in the Cordon. In the Cordon, Wolf leads the group and helps train new stalkers, preparing them for what they will face later in the Zone. They hold the small hamlet near Sidorovich's bunker, but most of the Cordon is under Military control. They are at war with the Bandit faction.
In S.T.A.L.K.E.R.: Clear Sky, the Loners are a full-sized faction, at war with the Bandits because they are tired of being harassed, robbed, and extorted. The faction is joinable, and their main base of operations is the farm north of the bridge and tunnel in the Cordon. Here, Scar experiences the beginning of the war with the Military in Shadow of Chernobyl. Most of the Cordon is under Stalker control, with units in almost every other location. They hold The Barrier in the Army Warehouses, keeping the Mutants and Monolith at bay.
In S.T.A.L.K.E.R.: Call of Pripyat, the Loners are again an organized Faction of artifact hunters. Their main base is Skadovsk, an old beached freighter. Many are employed by Beard, an artifact dealer. They are still at war with the Bandit faction. If Alexander Degtyarev gets in favor with the Loners, the faction size will increase, and Beard's prices will lower. Conversely, if that happens, Owl's prices increase. If Call of Pripyat ends in peace between Duty and Freedom, most members of those two factions leave to join the Loners.
The Mercenaries are a private military force operating within the Zone. They are professional soldiers who will do just about anything in the Zone, ranging from retrieval, assassinations, body-guarding, etc. Though, of course, it must be for the right price. Mercenaries are usually neutral toward other factions, as they are a source of income, unless they interfere with their operations.
In S.T.A.L.K.E.R.: Shadow of Chernobyl, they are not a true faction since most are employed by different employers, so most squads serve different goals than others. They are hostile to the player (as well as most factions, most notably the Ecologists.)
In S.T.A.L.K.E.R.: Clear Sky, the player takes the role of a lone Mercenary, Scar. The faction is not joinable (although Scar is a Mercenary by default), and some groups encountered are hostile; but most groups are neutral toward Scar, notably Leshiy and Hog's groups; and Leshiy appears to personally know Scar.
In S.T.A.L.K.E.R.: Call of Pripyat, the Mercs are employed to investigate the labs under Pripyat. At first they are neutral towards the player, however Jackal's group in Yanov - Skull and Black - become actively hostile to the player after investigating Yanov Powerplant. The only group that remains neutral is Hatchet's group.
The Ecologists are Ukrainian scientists sent into the Zone on behalf of the government, but seem to be affiliated with outside organizations. Their main purpose is the study of all aspects of the Zone, using scientific methods to further explain what the Zone is, and its purpose. The Ecologists are neutral to all factions, and are not involved in any of their conflicts. Due to the military's slipping grip on the Zone, the Ecologists rely on opportunistic Dutyers, Loners, and Mercenaries to provide them protection, and to perform errands that may require combat, since the scientists are better thinkers than fighters.
In S.T.A.L.K.E.R.: Shadow of Chernobyl, their base of operations is in the mobile lab at Yantar, where they investigate the Psi Emitter and research the Psi Protection Device. They are constantly under siege by Zombified Stalkers, and sometimes also by Mercenaries.
In S.T.A.L.K.E.R.: Clear Sky, they're stationed in the mobile lab at Yantar, and are just beginning their research on the Psi-Emitter and Psi Protection Device.
In S.T.A.L.K.E.R.: Call of Pripyat, they are stationed in a mobile lab at Yanov, and they've employed Loners and Mercenaries to protect the lab while they research Anomalies, Artifacts, and Mutant behaviors. Jackal's Mercenary group quits protecting them, and it is revealed that the mercenaries were actually trying to steal the scientists' information to progress their actual objective, which was to investigate the secret labs under Pripyat. It is Alexander Degtyarev's choice who to employ after they leave to protect the lab: Duty, Freedom, Spartacus's group, or Slasher's Mercenaries.
The Monolith were originally ordinary Stalkers who believed in the power of the Wish Granter. Prior to Clear Sky, the faction reportedly made an exodus to the Zone's center and disappeared. After the large emission during the events of S.T.A.L.K.E.R.: Clear Sky, they became active. The Monolith are the front line soldiers of the C-Consciousness, and would rather die than let any Stalker reach the sacred crystal. Although capable of higher reasoning and emotion, they nevertheless carry out orders with fanatic effectiveness. The Monolith faction has no allies, and actively attacks all other factions.
In S.T.A.L.K.E.R.: Shadow of Chernobyl, they are entirely hostile, the largest group in the Zone with the most advanced equipment. They are led by the C-Consciousness, but their leader in the field is Charon. Their main base of operations is the entire Pripyat town, but they also hold a base in the Sarcophagus.
In S.T.A.L.K.E.R.: Clear Sky, Monolith are again hostile, making their first appearance since when they were a neutral faction and ventured towards the center of the Zone. They are a fanatical, well-equipped faction, with huge numbers. Their main base of operations is in Pripyat (although the player never travels to Pripyat as this location was removed from the game.) Large numbers of Monolith are met in Limansk and the hospital, with even more at the NPP itself. It is unknown who the faction leader is at this time.
In S.T.A.L.K.E.R.: Call of Pripyat, Monolith forces are almost entirely hostile. While they may not be the largest group in the Zone, they are still the best-equipped. After the loss of the Brain Scorcher, the other factions have moved closer to Pripyat, and Monolith numbers have dropped. Here they are led by the Monolith Fighter.
Clear Sky is the most secretive faction within the Zone. The faction was disbanded after losing the majority of their manpower during the events in S.T.A.L.K.E.R.: Clear Sky. The Clear Sky faction was originally composed of former researchers of the C-Consciousness who broke away from them in order to conduct their own research on how to either destroy or contain the zone. The other members of the faction were ordinary stalkers who joined their cause for their own reasons.
In S.T.A.L.K.E.R.: Shadow of Chernobyl, the faction is disbanded due to their failure at the CNPP in the climax of S.T.A.L.K.E.R.: Clear Sky. The only known member of Clear Sky faction remaining here is Nimble, who has joined the neutral stalkers. The other possible living ex-Clear Sky member may be Scar, speculated to have become Charon, the combat leader of the Monolith faction.
In Clear Sky, the faction is a small group located within the Swamps. Most are ex-Military or Ecologists, researching the Zone. Their main goal is to stop Strelok from reaching the center of the Zone, because they believe that if he succeeds, the Zone will be destroyed. They are not joinable by the player, but are always friendly-neutral, as the player is unofficially part of the faction. They are actively at war with the Renegades and assist the player's push to Pripyat in the Red Forests and Limansk. (The Pripyat level itself was removed from the original game, so the transition to the CNPP happens immediately after emerging from the Limansk Hospital.)
In S.T.A.L.K.E.R.: Call of Pripyat, the faction is nearly non-existent. Nimble and Novikov are the only known surviving members of Clear Sky. The Player can obtain a CHN-3a Battle Armour suit from Nimble, and Novikov will recognize it on sight, and reminisce about his Clear Sky days.
A group of renegade Stalkers unaffiliated with any major faction, as well as cast-outs from other factions, they act as warbands and gangs instead. Although acting in the same way as Bandits by robbing and exploiting stalkers, the renegades are not under any formal leadership. The Renegade faction eventually dissolved after S.T.A.L.K.E.R.: Clear Sky, which is why they are non-existent in Shadow of Chernobyl and Call of Pripyat.
In S.T.A.L.K.E.R: Clear Sky, they are a small sub-faction of Bandits at war with the Clear Sky faction. They are not as well-equipped as and are fewer in number than the Bandit faction itself, and are easily dispatched. Their faction is not joinable.