If you attack, I will destroy the research results! You won't get my work!
Possessing a doctorate in biology, the Professor's main area of interest is new species of mutant animals. He finds and studies them, their behaviour and physiology. His study results are sent to researchers outside the Zone, however, some are shared with the Barkeep exclusively. He is very enthusiastic about the Zone (although, obviously, aware of its dangers) and considers it the greatest chance of increasing humanity's scientific knowledge and revolutionizing technology.
Kruglov is first encountered in the Wild Territory area, where he and his science team were ambushed by Wolfhound and his Mercenaries who want the research data he carries, believing that it can help them reach the center of the Zone. While the scientists are armed, they are by no means soldiers and are slowly picked off one-by-one. The mercs also shoot down a military helicopter that comes to their aid.
- Meet Kruglov / Lead Kruglov to Yantar and / or Meet Kruglov (both links relate to the same primary mission segment)
The player can choose to escort Kruglov out of the ambush in exchange for the flash drive the mercenaries were after, which can be sold to the Barkeep, and later, an SSP-99 Ecologist suit, provided the player talks to Professor Sakharov after completing the mission.
After escorting him out of the Wild Territory, he can be escorted once more to take psi readings during the Lab X-16 mission: Take radiation measurements, allowing the player to receive a better tuned, Functional psi-helmet. The adjusted helmet allows Marked One to endure the psi emissions for a longer period of time before being zombified.
If the player fails to escort him out of the Wild Territory, he will be replaced by Assistant Semenov, acting identically to him, only distinguished by the different suit, the latter one using an orange SSP-99 suit, while Kruglov's SSP-99M is green.
- There is a bug causing Kruglov not to follow player after one talks to him and suggests him to follow. This is probably caused by saving right before Kruglov asks Marked One to help him making him to fight like a usual NPC. The only way to avoid it is not to save before attacking mercenaries as there is no way to make Kruglov follow the player after this bug occurs.
- If this occurs, one can just kill Kruglov and take his flash drive–the quest won't be failed.
- The half of his squad who are supposed to spawn dead are alive and are quite effective in combat, killing the mercenaries with ease; but once you get to the second group of mercenaries before the Burner anomalies, the rest of his team drop dead or (occasionally) run and beg not to kill them.
- If Wolfhound and his crew are killed before or after you rescue Kruglov, then the Scientist crew will wander around the Wild Territory, unable to escort Kruglov to Yantar.
- The Zombie that spawns at the Burner Tunnel should not be a problem from a 'mission break' point of view, but a rare random spawn of Snorks near the tunnel entrance could overwhelm Kruglov if player is not fast enough.
- Near the end of the first escort mission, before the Burner anomalies in the tunnel, it is possible that Kruglov may freeze and not follow the player after he goes through the tunnel. It is also possible that he will go through the tunnel, but talking to him will crash the game.
- Another bug is that he may go through the anomaly tunnel unharmed, but then he will draw his weapon, aim at the tunnel, and freeze. These bugs can be avoided by going back to a previous save game and restarting the mission.
- This anomalous behaviour may also be caused by enemy units spawning randomly within the NPC's detection radius. Elimination of these units will end the anomalous behaviour and progress the game normally in the fully patched version.
- In the earlier versions of the game, it is possible to use following bug: after escorting Kruglov and protecting him from the mercenaries, one can simply press "Esc" after receiving flash drive and repeat it as many times he wants (making it equal to the other well-known bug in S.T.A.L.K.E.R.: Clear Sky). Every flash drive obtained can be exchanged for 5.000 RU from Barkeep.
- If one manages to keep Kruglov (or Semenov wearing an orange SSP-99 Ecologist suit) alive by killing all the attackers quickly then after talking to Kruglov he will reply normally but won't actually leave the area. Possible remedy–draw a weapon in his vicinity.
- There is a bug/exploit that allows player to ignore further main quest segments and complete the game. To do this, the player needs to rescue Kruglov in the Wild Territory and escort him to Yantar; there, one needs to kill Kruglov inside the bunker (the only possible way in vanilla game is to damage and kill him with grenades from outside the bunker). Sakharov will react as though Kruglov was killed during the measurements mission, and the player will receive a Not adjusted psi-helmet and subsequent instructions to loot Vasiliev's body.
- The same exploit applies to Semenov if Kruglov was not rescued/escorted
- As a bug/feature, Kruglov becomes hostile to player if one joins Freedom faction. In this case, he stands behind the second door of the bunker blocking the passage inside it, although his sticking out arms can be shot.
- In rare cases, he may attempt to shoot enemies that get too close to the mobile science lab. However, the door will not open and the player cannot make him budge until the assailants are killed.
- Professor Kruglov is the only living character wearing an SSP-99M Suit. Two more scientists in this suit may be found dead in the Red Forest location.
- Kruglov is the only NPC in S.T.A.L.K.E.R.: Shadow of Chernobyl that has an unstable rank: in the Wild Territory, he is Experienced, while in Yantar, he is already a Veteran.
- If the player is slow enough, mercenaries can eliminate Kruglov's guard and get right to his face. In this case, Kruglov will stand still allowing them to kill him without any resistance from his side.
- Ecologists protecting Kruglov can sometimes stand still, not in a battle position, and, more interestingly, use mercenaries' voice-overs. To do this, one needs to revive any of them by giving a medkit after mercenaries are dead but before talking with Kruglov.
- Kruglov does not react to his group members' death caused by the player.
- If player reloads the save he/she made right before getting to the construction yard, Kruglov can begin shooting at mercs that will do nothing until player triggers the "Ambush!" phrase from his/her "ward."
- It is strange that Kruglov uses his pistol while having TRs-301 in his inventory. However, Kruglov will pick up anything equal or weaker than the Akm 74/2.
- Despite Kruglov stating that he is a bad fighter, he actually has a huge advantage on mercs and zombified stalkers as he is wearing a good armour himself while still being capable of headshoting and killing an enemy from range with his Walker P9m. If given a better weapon that he can pick up, Kruglov will need nearly no player's protection.
- The scene of Kruglov talking with Sakharov about measurements always repeats as player enters Yantar location.
- During the Take radiation measurements mission, Kruglov may be killed by zombies after the blowout while the player is still waking up, thus failing the mission even though the player was unable to do anything.
- Kruglov's flash drive contains information that the source of psy radiation is located in the center of Yantar lake, while in actual game, it's hidden in X-16. This is probably due to the earlier versions of the game, where the source was really located in the middle of the lake.
- He will never take off his suit, even when in the safety of the mobile lab. Because of this, it is unknown on what he actually looks like.
- S.T.A.L.K.E.R.: Shadow of Chernobyl, Kruglov's dialogue: My name is Kruglov. I am a professor of biology, I study the Zone. Yesterday, for example, I found an animal of particular interest - Antropomorphus Dendromutantus Vulgaris. I mostly find and document new species of mutant animals, their traits and distinctive features. The information is then thoroughly studied and transferred to the outside world. Some of it, of course, goes to the Barkeep. My discoveries have helped to save the lives of many stalkers. I was just transporting the results of my latest research to the laboratory near Lake Yantar when the helicopter came under fire.
- S.T.A.L.K.E.R.: Shadow of Chernobyl, stable_bio_name.xml; id=ros_kruglov_bio: Ph.D. in biology. Studied pathogenic mutations in animals outside the Zone. Came to the Zone to study blind dog mutations.
- S.T.A.L.K.E.R.: Shadow of Chernobyl, Kruglov's dialogue: The Zone is a wonderful gift to humanity. Of course normal existence here is not possible due to the high radiation levels, and aggressive mutants. All of these things are obviously extremely dangerous but they are also things of great scientific value. The Zone is almost a natural experiment, a treasure for scientists! The extent to which humanity's knowledge could be increased through the study of the Zone is unfathomable. Technology, medicine, new plants- medical and edible, biotechnology, cures for incurable diseases…anything! Perhaps we can solve the food problem for the entire planet. If people didn't interfere, science could lead humanity into a new Golden Era!