Expert is a rank in the S.T.A.L.K.E.R. series. It is the highest rank NPCs can have.
Experts are the best stalkers in the Zone with years of experience and equipment better than most other stalkers. Expert stalkers can belong to any faction, although they appear more often in the Duty, Freedom, and Monolith factions. Experts use heavy armour such as exoskeletons and tend to use rather exclusive weaponry, including the Tunder S14, the RP-74, or the Vintar BC, for example.
Experts in Shadow of Chernobyl are primarily found in the northernmost zones such as the Red Forest, Pripyat, the Chernobyl Nuclear Power Plant and the inner areas. Duty experts can be seen guarding General Voronin's bunker, and it is possible to spot one at the entrance of the Wild Territory. Freedom experts can be seen at the faction's HQ in the Army Warehouses, and sometimes at the Barrier. Monolith experts spawn throughout the Zone, mostly in the Sarcophagus. Pripyat is almost exclusively populated by experts.
Experts appear by default in Limansk and the Limansk Hospital. As part of the Faction Wars game mechanic, experts will become much more common once a faction has gained a good amount of resource, that can be acquired by conquering territories. Experts can be found in the factions bases as well.
Experts will not spawn by default and only spawn after the player has completed the Pripyat 1 main mission. Monolith and Zombified stalkers experts will commonly spawn throughout the game by default, but experts from other factions will not appear unless the player has completed Pripyat 1.