No. 4

No. 4 was a mysterious individual who gave instructions via Codec to "Jack", a participant of various VR missions. No. 4 was capable of impersonating other people, as evidenced by his mimicking of Mei Ling several times during one mission. Upon completing the course, No. 4 congratulated Jack.

Behind the scenes
No. 4 appears in the VR special mission stages in Metal Gear: Ghost Babel. He instructs the player via Codec, and also provides commentary on the events of the Galuade Incident, including things not made immediately apparent within the main game itself. His reference to the player as "Jack" alludes to the events of Metal Gear Solid 2: Sons of Liberty, in which the VR-trained protagonist Raiden is named Jack. No. 4's behavior also alludes to the shadowy organization the Patriots.