The reason I've survived in this place as long as I have is that I always keep my word. You screw a client in this place, and you're pretty likely to find a knife in your back real quick.Sidorovich
He is known throughout the Zone and the underground market for being the only reliable connection to the zone of alienation from the outside world. He achieves this with the help of the army inside the Cordon. There is a common saying amongst Stalkers that if Sidorovich can't complete your shopping list, no one in the Zone can.
Sidorovich was one of the first people to enter the Zone . He conducts all of his business in an underground bunker located in the Cordon, near the rookie village. He handles nearly all of his business in the bunker, saying that he's not the fighting type and won't survive long outside.
You got away from the Military, you lucky devil! I've got a feeling there's a purpose that you are here...Sidorovich
In S.T.A.L.K.E.R.: Clear Sky, Sidorovich has a smaller role than in the first game. Scar visits the trader after leaving the Great Swamp, asking Sidorovich for information on Fang. This leads to Scar getting involved in the conflict between the Loners and the Military in order to locate a small crate of exotic loot. After returning the loot box to Sidorovich, the trader reveals what he knows about Fang; after which he is available for normal trade and can answer a few questions about himself.
Sidorovich will also give a discount to Scar once he completes his job of retrieving the package, albeit even with the discount, his products are still expensive as you'll get better prices from faction traders even without joining or even being friendly with them. He will however offer the highest price for artifacts, ranging at a whopping 90%. It is a very good idea to trade your expensive artifacts to Sidorovich to get the highest value for your money.
Curiously, Sidorovich's appearance changes rather distinctly between the games. He has hair in Shadow of Chernobyl, where as in Clear Sky he is completely bald. Also, he uses a desktop computer in Clear Sky; while in Shadow of Chernobyl he uses an Asus brand laptop, likely replacing his old computer with a newer one after getting richer.
Shadow of Chernobyl
So Marked One I saved you and I'm not gonna pretend I did it to win favors upstairs, you do some jobs for me and we're even. Besides, keeping you busy might be a good way to deal with your amnesia.Sidorovich
In S.T.A.L.K.E.R.: Shadow of Chernobyl, Sidorovich is the first person the player encounters. In the opening cutscene, the Marked One is taken into Sidorovich's bunker and examined by the trader before waking up. Directly thereafter, Sidorovich provides a short game tutorial and sends the player on his first mission. His, and Barkeep's, ultimate goal is to open the road to the center of the Zone.
From there, Sidorovich remains a steady fixture in the main quest, providing information at crucial points in the story and occasionally getting directly involved again. Most notably, the player is told to return to Sidorovich after completing the raid on lab X-18, after which there is a special albeit optional mission which involves stealing a briefcase from the cordon military outpost.
In the canon ending to Shadow of Chernobyl, as Strelok escapes from the Chernobyl NPP via teleportation gates, he teleports into the trader's bunker for a split second, causing Sidorovich to jump off his chair and cry out in shock: "Marked One, what the hell?!". His fate remains unknown after that. He is not present in any of Call Of Pripyat (apart from a small mention), though it is assumed that he remains the same trader that he was.
- Sidorovich will buy artifacts for 65% of their base value, ammunition for 50%, weapons for only 20% (with weapons addon for 45%), armour for 65%, medical consumables for 75%, food for 20%, unique equipment for 65%. He is not interesting in buying mutant body parts. 
- He has following items in stock:
- Starting stock:
- He may offer 5.45x39mm FMJ ammo alongside with a rare modified "Tunder" 5.45 with a chance of 10% for a price of 20000RU (two times the base cost of the weapon)
- Mercenary suit - 10% chance for twice the base price.
- Up to 5 bandages - 60% chance for each for twice the base price.
- Up to 5 medkits/Anti-rads - 30% chance for each for twice the base price.
- Up to 10 loaves of bread, cans of Tourist's Delight, or Diet Sausages - 50% chance for each for twice the base price.
- Up to 10 bottles of vodka, cans of Energy drink - 30% chance for each for twice the base price.
- Starting stock:
Sidorovich hands out a number of missions as listed below:
- Item retrieval
- Mutant body part retrieval
- Camp elimination
- Stalker assassination
- Mutant elimination
Call of Pripyat
Sidorovich only gets a small mention in Call of Pripyat. His name pops up when asking stalkers where to find tools, and they answer by saying that the last place they saw tools was back in Sidorovich's bunker.
Shadow of Chernobyl
- "So Marked One I saved you and I'm not gonna pretend I did it to win favors upstairs, you do some jobs for me and we're even. Besides, keeping you busy might be a good way to deal with your amnesia."
- "What are you standing there for? come closer."
- "Not bad, some pretty good stuff you got there."
- "That's my boy, you made my day."
- "What is this shit?"
- "Got anything valuable?"
- "You got the loot?"
- "Good hunting, Stalker."
- "Marked One, what the hell?!"
- "Hello, anyone home?"
- "Come on, tell me what you got for me!"
- "Relax, don't be shy, what brings you here?"
- "Don't just stand there, eh!"
- "Hurry up with that case, alright?" - After receiving the mission to find the loot
Originally, Sidorovich's bunker had much worse quality and the man himself had a wildly
different appearance. Instead of the balding fat trader model, it was a fat, sweaty model with a pudgy face and bright blonde hair in a white tanktop, jeans and missing his left hand and always carrying a shotgun. He was also known as "Toad" Or "The Dealer". In build 1537, he has a model.
Sidorovich now received his final model, although his menu GUI is still the old "Dealer".
Sidorovich now looks as he did in Build 1844 but his voice drastically changes. In Build 1935's voice files, his voice sounds like that of a stereotypical old man with a bit of an accent.
- In the back of his bunker the player can see a fully upgraded Tunder S14 . It is unknown why he has it, since he is never seen wielding a weapon, but he could have received it through trading and is displaying it as a trophy.
- He may sometimes sell a 5.45x39mm Tunder S14.
- In Shadow of Chernobyl, if the Marked One selects the trade option and exits out without giving or buying anything, Sidorovich will grumble and complain.
- Humorously, if one is to throw a grenade before using the teleportation gates, Sidorovich can be "killed" by the explosion in Shadow of Chernobyl.
- This is most likely a glitch or an oversight by the developers. If return to Cordon in free play (especially playing with mods like Complete Mod), he can be seen that he is still alive.
- Andrey Podubinskiy, Sidorovich's voice actor, has unfortunately passed away on March 23 2018, at the age of 74.
- In his own words in Clear Sky.
- Shadow of Chernobyl 1.0006; trade_trader.ltx
- Prices are calculated based on the following formula: ((first_value+second_value)/2)*100 presented on Stalker SDK modding wiki
- Koan's gift, OldDesigneDocument Story.doc