Silent Basilisk was a former member of the Hamid group of the Mujahideen stationed at Da Smasei Laman. His unit was wiped out under mysterious circumstances shortly after receiving the Honey Bee secret weapon from their CIA handlers, with him being the sole survivor. The Soviets eventually became privy to the CIA weapon and attempted to interrogate him for its location. As he was mute, however, he could not respond to their questions verbally. Eventually, the Soviets decided to have him physically lead them to the weapon. However, Venom Snake proceeded to save him from his captors, to which he promptly returned the favor by giving his group, the Diamond Dogs, who had been contracted by the CIA to recover the weapon before it fell into enemy hands, the location of the Honey Bee by pointing to it on a map. Miller was suspicious that his being mute had some connection to his being the sole survivor of the Hamid group at Da Smasei Laman. This was later proven to be true when he managed to survive two vocal cord parasite epidemics at Mother Base due to being mute.
Behind the scenes
The Hamid Mujahideen survivor is a character in the mission "Where Do the Bees Sleep?" in Metal Gear Solid V: The Phantom Pain. The player can either rescue him as a side objective, or otherwise allow the Soviets to lead him to the Honey Bee weapon and tail them. After the survivor is recruited, he is code named Silent Basilisk and is one of the few staff members unable to be dismissed by the player. He also cannot be seen and interacted with while on Mother Base.
If the player reaches Silent Basilisk before he's put in the car, a cutscene would be triggered where he shows the location of the Honey Bee to Venom Snake. This also happens if the player removes him from the car and places him on the ground before fultoning him.