Nikolai

Biography - Modern Warfare

In the mission "Blackout", Nikolai is introduced as an informant for the S.A.S. who was previously behind enemy lines in the guise of an Ultranationalist. Nikolai is a former Soviet Army Senior Sergeant. The mission involves Captain Price and his team going to rescue Nikolai before he can be executed by the Ultranationalists for being a spy. Without Nikolai, a good majority of the events in Modern Warfare could not have taken place due to his intel, such as the initial cargo ship mission entitled "Crew Expendable". After he is taken aboard a  UH-60 Black Hawk helicopter to be extracted, this plan is cut short as it is shot down before they were able to leave the area. He is then forced to fight alongside Price's S.A.S. with nothing but an AK-74u that I took right after this initial rescue. Once the team get cover fire from an AC-130, he is finally extracted by another helicopter to a safe house in Hamburg. His last mention in Modern Warfare is in a cutscene where Nikolai gives the S.A.S. the coordinates to a safehouse in Azerbaijan, the possible whereabouts for Khaled Al-Asad. 
 

Biography - Modern Warfare 2

Nikolai returns in Modern Warfare 2, and first appears in the mission "The Hornet's Nest". Members of Task Force 141 (including Soap, Ghost, and Roach) have been stranded in the Brazilian favelas as no air-based extraction could be given to them, so the 141 have Nikolai come in to rescue them. The initial landing zone is deemed 'too hot' by Nikolai due to heavy RPG fire from the local militia, so a make-shift secondary extraction is made after Soap orders Nikolai to 'wave off'. As they make their way to the extraction, Roach fails to make a jump from one roof to another, causing a delay in the extraction. As Roach makes a quick escape, Nikolai readys his Pave Low helicopter for Roach to jump across to the ladder being dropped from the Pave Low by Soap. 
 
In "The Enemy of My Enemy", Nikolai extracts Captain Price and Soap from the boneyard in a C-130 by positioning it on the runway for Price and Soap's jeep to drive into the back of, making for a lucky escape. Nikolai then drops Price and Soap off at Site Hotel Bravo (in "Endgame"), and despite him being told that it would be a one-way flight, Nikolai returns to extract the two knowing the dangers he now faces. 
 

Trivia

•  Nikolai's name is still unknown, as he is referred to as "Codename: Nikolai" in Call of Duty 4: Modern Warfare.
• In "The Enemy of My Enemy" ( Modern Warfare 2), he says that he's not getting paid enough to crash the C-130 he is piloting. This potentially means that he is being hired by Task Force 141 as opposed to being a member. It could also be a simple remark about his general salary, or just a joke.