Natalya's former lover who provides information for her and Crypto to use to uncover the conspiracy surrounding the KGB. Crypto is jealous of him because of his own feelings for Natalya. Sergei, however, does not share Crypto's hatred; contrarily, he understands Crypto's feelings for Natalya, but looks down on him as though he were a child.
After being infected with Blisk Spores, Sergei is never heard from again.
- His truck is a re-used Army truck from the first game.
- His screams are also recycled civilian screams from the first game.