In Call of Duty 4: Modern Warfare
Nikolai (Russian: Николай) is the code name of a Russian informant amongst Imran Zakhaev's Ultranationalists, and an ally of the S.A.S.
In events before the mission "Blackout", Nikolai has been detained by the Ultranationalists under suspicion of espionage. The S.A.S team under Captain Price must find and rescue him before he is executed. He had been informing the British from the Ultranationalist camp until his cover was blown. He helped to start the entire chain of events in Call of Duty 4: Modern Warfare, as it was he that supplied the intel for the cargo ship mission.
In "Hunted", the Black Hawk carrying the extracted team is shot down over hostile territory, and he is forced to fight alongside the team with only the AK-74u he has been found with (in some instances, Price is seen giving it to him). Finally, under cover of AC-130 fire, Nikolai is evacuated by a second helicopter to a safe house in Hamburg, and his last mention in the game is a loading cutscene in which he sends the SAS the coordinates to Khaled Al-Asad 's safehouse in Azerbaijan.