From the Metal Gear Wiki

Nikolai Stephanovich Sokolov
Nationality	Russian
Affiliations	Developer of the Shagohod
Current status	Unknown
Game series	Metal Gear Solid
Appears in	Metal Gear Solid 3
Created by	Hideo Kojima
English voice actor	Brian Cummings
Japanese voice actor	Naoki Tatsuta

Nikolai Stepanovich Sokolov is a Russian scientist who defected to the US shortly after the beginning of the Cold War. He was the head of the OKB-754 before he defected.

October 16, 1962. President Kennedy received word that the Soviets were in the process of deploying intermediate-range ballistic missiles in Cuba. The president demanded that the Soviets dismantle and remove the missiles. At the same time, he announced a naval blockade to prevent further missile shipments from reaching Cuba. But the Soviets didn't back down, instead placing their armed forces on secondary alert. Soviet transport ships carrying missiles continued on course toward Cuba. US and Soviet forces went on alert for an all-out nuclear war. Frantic negotiations were conducted through the UN's Emergency Security Council and unofficial channels to end the hair-trigger standoff. Finally, on October 28, the Soviet Union agreed to remove its missiles from Cuba. And so the world avoided a nuclear holocaust. But in exchange the Americans had to surrender Sokolov over to the Russians. He was then placed in an abandoned research facility near the OKB-812, and was guarded by soldiers in order to prevent Colonel Volgin from kidnapping Sokolov to make him work on the Shagohod.

Sokolov showed fear to his enemies but also presented courage, when Tatyana was being electrocuted by Colonel Volgin...Sokolov threatened that he would not work on the project if she is hurt, but was proven wrong when Colonel Volgin threatened him. He has no shame for what he does but has guilt that his gifts are being used to bring destruction to mankind. He loves his family and shows affection towards people who are being hurt by others.

[edit] Operation Snake Eater

After Naked Snake succeeds in rescuing Sokolov he is quickly confronted by The Boss who tells Snake of her defection, she then takes Sokolov as a "gift" for Volgin. They also take Tatyana (a.k.a. EVA) who is Volgin's lover. One week later, Tanya requests the data of the Shagohod from him, and so he gives it to Tanya thinking it would be handed over to Kruschev (unbeknowingst to him would actually be given to the People's Republic of China). Snake attempts to rescue him again, but he informs Snake that he's to late as the Shagohod is already finished. Snake contradicts him however that if the liquid fuel tanks are destroyed along with the Shagohod, there would still be hope for the safty of the world. Just when Snake was going to see him out of Grozni Grad, Sokolov refused as he would probably sent to the Gulaugs as Kruschev has abandond him. Snake then asked him about coming to America as planned but retorts that, as a weapons scientist he'd only be used on the West's side instead and would rather not go anywhere but only requests that his be kept safe. After Volgin feels Sokolov has served his purpose, and finding him with the CIA spy Snake, Volgin interrogates/tortures and apparently kills him for who he'd been talking to and who he'd given the data of the Shagohod to.

[edit] Ghost

As Big Boss would later learn, Sokolov was not dead. He had, in fact, been captured by Soviet authorities in the wake of the Shagohod incident. Imprisoned in a work camp, he was eventually rescued by Gene, and taken to the United States upon where he was reunited with his family.

But he could not long escape his life as a weapons scientist. He joined Gene's research team and participated in the design of the Metal Gear prototype RAXA. He was taken to Army's Heaven, but realizing that Gene was a maniac, plotted to stop him. This opportunity came in the form of Big Boss' infiltration. Under the alias "Ghost," Sokolov provided Big Boss with information over the radio, at one point allowing him to believe that he was Granin. Eventually, he revealed himself, and aided Big Boss in the destruction Metal Gear. He is also, at one point, recruitable.

Metal Gear Solid 3: Snake Eater Characters
Naked Snake — Major Zero — Para-Medic — Sigint The Boss — Colonel Volgin — Ocelot — EVA The Pain — The Fear — The Fury — The End — The Sorrow Sokolov — Granin — Raikov

Metal Gear Solid: Portable Ops Characters
Naked Snake — Roy Campbell — Jonathon — Para-medic — Sigint Null— Gene — Python — Cunningham — Elisa and Ursula Colonel Skowronski — Sokolov — Ocelot — EVA — Major Zero — Raikov Teliko — Venus