- "Allow me to introduce: Sergei Kozin, the monster of Magadan!"
- — Viktor Reznov to Alex Mason upon first meeting Sergei.
Sergei was a prisoner of the Vorkuta gulag. Nicknamed the "Monster of Magadan", he possessed brute strength, tackling two guards at once and killing them both with his bare hands, killing another guard with a pickaxe uppercut, helping Viktor Reznov to push a fully loaded mine cart and body slamming on an armory locker door to crack it open. He also has the hulking build to fit the name; apart from that, little is known of him.
Sergei was seen in the mission "Vorkuta", as part of the band of prisoners who took part in the uprising. He appeared on the way to the elevator, pushed the coal cart with Reznov, and disappeared after he opens the arms locker. He reappeared before the gate to main armory. He used his sheer strength to hold the shutter open for Mason, Reznov and the other prisoners. However, just as Mason was able to get through, Sergei was shot by one of the guards, resulting in gate coming down on top of him, killing him.
- An image of Sergei and the Vorkuta escape is an optional design for the Playercard.
- Sergei's base model are reused as Prisoner Zombie in Zombies mode.