Military
Soldiers are regular army units. They guard the approaches to the Zone's closed territory, patrolling the perimeter, shooting mutants, and capturing looters. Army special forces are elite units. They are typically deployed to the Zone to conduct rescue and special operations.
The Ukrainian Armed Forces are concentrated primarily along the Zone's perimeter, such as the Cordon, the Dump, and the Agroprom Research Institute. They also appear in large numbers near the Chernobyl Nuclear Power Plant itself during the storyline.
Military Stalkers
Soldiers who have undergone special training after serving in the Zone, or stalkers who have signed a contract with the army. They are equipped with a large amount of auxiliary equipment and are well armed and equipped. They are primarily used to study the causes and consequences of the disaster and also to map the Zone. They can travel alone or in groups of up to five. They don't allow ordinary stalkers to approach them—they immediately open fire.
Corrupt stalkers work for the government. They can be encountered near the end of the game, in the Pripyat and Chernobyl Nuclear Power Plant locations.
Mercenaries
The most mysterious and secretive group in the Zone, whose existence many don't even believe. Some regularly employ the services of mercenaries: professionals in their field, they can quickly deal with any stalker and can even completely eliminate a small group. For their services, they apparently charge considerable sums in money or artifacts. The location of this group's base remains a mystery; it is apparently located somewhere deep within the Zone.
This group doesn't have its own base (due to the developers' fault, of course!). They can be found at the Rostock Factory in the Wild Territory and at the Army Warehouses, in the northwest corner of the location, near a passage that, according to many gamers, should lead to another location (which, by the same developers, was cut).
The Monolith
is a group more reminiscent of a religious sect. Its members believe that an evolutionary crystal of extraterrestrial origin—the Monolith—rests at the center of the Zone. Most stalkers despise the Monolith's adherents, considering them mad. Since its formation, the group has hindered stalkers' advance toward the center of the Zone, citing their ill intentions toward the Monolith. Rumor has it that the Monolithists have a large base somewhere closer to the center of the Zone, but its exact location is unknown to anyone but the group members themselves.
These cultists infest the Radar with its laboratory, Pripyat, and the Chernobyl Nuclear Power Plant. It's worth noting that, in the latter location, if you complete the "correct" playthrough, you can wander through the cultist base. The main headquarters of this group was planned for the Pripyat location, beneath the theater, where Charon was supposed to be the leader.
Duty
is a clearly paramilitary group distinguished by strict discipline: its members practically live by a charter. Only Duty representatives do not trade the unique creations of the Zone with the outside world: according to rumors, all artifacts found by these people are handed over to scientists. Each Duty member considers their primary goal to be protecting the world from the Zone's influence. Most of the group's operations involve exterminating monsters, so Duty raids often relieve ordinary stalkers of many pressing problems. They have a long-standing and bitter feud with the Freedom group.
The advance group guarding the passage to the Bar can accordingly be found in the Dump location. The bulk of the fighters are stationed in the former. They periodically venture into the Wild Territory location to clear out groups of bandits and mercenaries. Another detachment of highly zealous Duty members is stationed in the Army Warehouses. Towards the end of the game, members of this society will help break through Pripyat.
Freedom
Anarchists and daredevils who have declared themselves freedom fighters within the Zone, and therefore are in constant conflict with army units, military stalkers, and the "Duty" group. Freedom members believe that information about what is happening in the Zone cannot be hidden from humanity, thus challenging the government's monopoly on the local secrets and wonders.
They consider the Army Warehouses location their home.
Zombified Stalkers
Those who have been exposed to emitters in Yantar or other sectors for extended periods. Careless stalkers quickly go mad, turning into wandering half-corpses. Many of them roam the Zone, some even reaching the perimeter. Regardless, it's impossible to help them: the process of personality destruction is irreversible. Although zombified stalkers can still use their weapons, they are quite stupid. When encountered, they can be heard muttering fragments of phrases under their breath, which, however, are completely meaningless. Over time, zombified stalkers completely lose all their previous skills and turn into zombies. They are typically very aggressive and pose a serious threat in large groups.
Usually, unsuccessful stalkers turn into zombies, and this only occurs in the Yantar and Radar locations.
Bandits
Representatives of the criminal underworld who came to the Zone for various reasons: to make money selling artifacts, to evade the law, or to buy or sell weapons. The Zone is home to many such elements, ranging from street urchins to serious criminals. Most of them are organized into gangs. Although there is still no unified gang organization in the Zone, they are a major nuisance to ordinary stalkers.
These guys are clearly not from far-flung places. They appear in small groups in all locations up to the Radar, and only in the Dark Valley do they have a permanent base, led by Borovoy.
Lone
Stalkers are those who explore the Zone alone. They are the majority, as group membership takes up
precious time, thereby reducing earnings; furthermore, some are simply naturally inclined toward
solitude and independence.
Lone Stalkers are encountered throughout the entire area leading to the Radar, primarily in the Cordon, the Dump, and the Bar.
Ecologists
and Scientists belong to the Mobile Laboratory. It looks like a small metal bunker with small tinted windows. It can withstand almost any damage known to man of any kind (editor's note: even a nuclear strike?). It can be switched to autonomous mode for several months, for which it is equipped with reliable life support systems. It is delivered to the Zone by cargo helicopter. The laboratory staff (Ecologists) never allow outsiders past the outer airlock, so no stalkers have ever penetrated the laboratory.
Scientist rats are encountered in only two locations: in the Wild Territory, according to the story, and in Yantar, where they maintain a mobile research base. The smallest group in the Zone consists of
Sakharov, Kruglov, and the half-decomposed body of Vasiliev...