The assassin known as Tixij(“Quiet” in Russian) was trained heavily in the hunting and killing of human beings. She first appeared in the Metal Gear timeline in 1980 working for the villainous organization XOF. Little is actually known about her largely because of her trademark silence. It is unlikely that her name is actually Quiet and more likely that this is a moniker she adopted based on what Russian troops called her. Her real name would have no use in her line of work and a codename more easily strikes fear into the heart of the enemy. The XOF used to be an even more covert assist organization to the CIA’s FOX organization in the 1970s. Due to her apparent age, it is unlikely that Quiet was active then. Instead, she worked for XOF during a time when it was a covert strike force for the Shadow Government organization Cipher. As such, she reported directly to the madman Skull Face and supported his schemes directly.
Quiet first appeared during the hospital raid that sparked the Phantom Pain incident. She was sent to infiltrate the hospital in Cyprus to murder the legendary folk hero/mercenary known as Big Boss. After killing the doctor and nurse, she radioed in to explain that Big Boss’ roommate had seen her face. She went on the attack again but the two men fought back. In the end, Quiet was doused with rubbing alcohol and set on fire. She crashed through the hospital’s window. She survived but obviously sat out the rest of the hospital raid as The Man on Fire, Tretji Rebenok, and the rest of the XOF forces also failed to kill Big Boss and his new ally.
The next time that Quiet appears is through rumors overheard by Venom Snake (aka Big Boss) as he engaged in missions in Afghanistan in 1984. She was tasked by Skull Face to eliminate any Russian military officers who opposed Skull Face’s development of a giant killer robot (Metal Gear) named Sahelanthropus. When Venom Snake got too close to the development site of the Metal Gear, Quiet spotted him, and the two engaged in an epic sniper duel. Quiet planned to finish where she started back in Cyprus. However, this time was far different as she now had super speed and was extremely durable. It took several shots from his firearms to take down Quiet. Choosing to spare her, he took her back to his base off the coast of the Seychelles.
During the process of retrieving her alive, Quiet actually defends Snake by shooting down a fighter jet with her sniper rifle.
This is where it gets weird.
After she is captured, Quiet is studied by Venom Snake’s mercenary group the Diamond Dogs. When she was taken out by Snake, Quiet was barely clothed and the mercenaries attempted to change her clothes. She fought back like a cornered animal and took out the soldier trying to clothe her. After further study and story reveals, it was found that Quiet had been healed from her injuries in Cyprus through the use of Parasites (the main sci-fi MacGuffin of the game). The process had fundamentally changed her body. Her lungs had been burned up but the healing process compensated for that when it regrew her skin. She now breathes and drinks water through her skin so clothing would suffocate her. She also no longer needs to sleep or eat as she basically photosynthesizes more or less.
Note from me: Yes, Hideo Kojima explained that his assassin character wears a bikini top and torn low-rise pants because of a medical condition. This is a bit of a copout but it strangely fits in with all of the other weird stuff that Kojima has put in the franchise over the years. It also helps that although Quiet is silent, she is an interesting character.
After a period of imprisonment which Quiet seemed apathetic about, it was found that the only thing Quiet was actually interested in was Venom Snake. Eventually, Snake agreed to take her out on missions as his sniper support. He is able to give her commands to do recon or to cover him during infiltrations of bases and villages. (For me, Quiet has become a comforting presence as I know she will be there to back me up if something goes wrong.) In between missions, Quiet is returned to her cell (with plenty of air and sunlight) where she lays face down with her top undone.
Over time, Quiet comes to respect Snake and adjusts to his tactics. While initially she only uses lethal ammunition, she can be convinced later to adopt the use of tranquilizer darts for her sniper rifle. This jives more with Venom Snake’s tendency to leave enemies alive for interrogation and/or conversion to his cause. Quiet becomes more selfless as she evolves and seems to care for Snake and his friends.
Of course, why she remains silent is a whole other story.