The Raikov mask was a sophisticated mask created by Sigint that was based on that of GRU major Ivan Raidenovitch Raikov. Naked Snake made use of this mask during his missions into Tselinoyarsk in 1964.
During the Cold War, a CIA operation was planned where an agent would be inserted into the Soviet Union, pose as a GRU officer, infiltrate a Soviet installation, and steal classified documents. Sigint was called in to develop the mask, and succeeded in installing a perfectly functional blinking mechanism, although he was unable to make the mouth move, seeing it as being beyond even his capabilities. However, the mission was cancelled before the mask could see use, and Sigint was ordered to dispose of it by Major Zero. Sigint successfully protested against the decision, largely due to his accomplishments, and it was instead placed into storage.
In August 1964, Major Zero decided to put the mask to use in the Virtuous Mission, by having FOX member Naked Snake use it to conceal his identity from the gunship crew. Snake later learned from Zero about the mask's history, after HALO jumping into Tselinoyarsk, with Zero commenting that it was "rubbing him off the wrong way." Although Snake felt he was unlikely to cross paths with the mask's model, due to being in the KGB's sphere of influence, Zero suggested he "beat the crap out of him" in the event that he did. In addition, Zero suggested that Snake not wear the mask while rescuing Dr. Nikolai Sokolov, apparently because the scientist disliked Raikov.
A week later, during Operation Snake Eater, Naked Snake took the mask with him again to Tselinoyarsk. He ultimately used the mask for its intended purpose when infiltrating the military fortress of Groznyj Grad, where Major Raikov himself was stationed. Snake knocked Raikov unconscious and stole his uniform in order to disguise himself as the Major, and access the west wing of the fortress. However, the mask was eventually removed by The Boss shortly after GRU colonel Volgin deduced Snake's true identity (as Volgin was Raikov's lover). The mask was later recovered by fellow spy EVA, along with the rest of Snake's gear, when Snake escaped from Groznyj Grad. However, he was unable to use the mask effectively the next time he infiltrated the fortress due to the personnel's prior knowledge of his previous disguise attempt, and was also missing his officer's cap. The mask was left behind in Tselinoyarsk, after Major Ocelot threw Snake's backpack from the WIG aircraft as it took off.
Behind the scenes
The Raikov Mask is a camouflage item used in the game Metal Gear Solid 3: Snake Eater as well as Metal Gear Solid 3: Subsistence and its HD and 3D remakes. Hideo Kojima inserted the mask into the game as a way to allow fans of the series who had a lot of favor towards Raiden to technically "play" as him. In a director's commentary, Kojima noted that the mask's lack of a functional mouth resembles E0 (Enemy Zero) and D2 (D no Shyokutaku 2).
If the player selects the option "I Like MGS2" when starting a new game, the opening cutscene will feature Naked Snake wearing the mask. In addition, an extra scene will feature where Zero comments that he is free to remove the mask due to the gunship crew not watching, with Snake agreeing. There were also plans to have differing responses from the depressurization crew member depending on whether the player was wearing the mask in the opening or not, but it was either cut from the final version or remained exclusive to the Japanese version. During two radio conversations, Zero will comment on his dislike of the mask (and in one case, the entire disguise). This is in reference to the fan controversy of Raiden's creation in Metal Gear Solid 2, whom Raikov, the model the mask, himself was based on for similar reasons.
Wearing the Raikov Mask in instances prior to wearing the uniform will result in Snake being spotted easily. In addition, if the player tries to wear the mask when attempting to enter Sokolov's area in Rassvet during the Virtuous Mission, Sokolov will react and tell him not to enter, warning him as well.
If the player contacts Para-Medic while wearing the mask, she'll briefly end up startled at someone apparently not Snake contacting her before Snake assures her that its him, and she'll mention that the mask reminds her of a Venusian before clarifying that she meant "the other kind" and not the "crab kind." This was in reference to the 1960s film It Conquered the World, which featured the main antagonist as a crab-like alien from Venus. A similar reference to that film character was made in the Japanese version of Metal Gear Solid 2 by Emma Emmerich (in the English version, it was changed to "Venus in Cancer").
If the player is spotted by Raikov while wearing the Raikov Mask and the scientist disguise, he won't sound an alert, but he will give one of two reactions: He'll either comment that Snake is "beautiful" while staring longingly at Snake, or he'll briefly react and then say "Hey!" before grabbing Snake's testicles.
If the player tries to wear the Raikov mask after infiltrating Groznyj Grad the second time, the mask's right eye will be permanently closed, owing to Snake's heavily damaged eye that necessitated his use of an eye patch. Raiden, (the character Raikov was based on) would later lose his left eye in the prologue of Metal Gear Rising: Revengeance.
The mask can be used to distract Volgin during Snake's battle with him, allowing the player an opportunity to attack. This use is a suggestion of Para-Medic's if she is contacted by radio, although Snake is confused as to why it would work, remaining oblivious to Volgin's and Raikov's relationship even after Volgin's sexual advance on him when he was impersonating Raikov.
In Metal Gear Solid, Decoy Octopus uses a mask to successfully impersonate the DARPA Chief, a character later revealed to be Sigint in Metal Gear Solid 4: Guns of the Patriots, himself the creator of a realistic mask.
Coincidentally, the realistic masks used by Snake and Octopus are similar to the masks used in the Mission Impossible films.