Jack

Jack, also known as Subject Zero, is a notorious criminal whose crimes include piracy, kidnapping, vandalism and murder. She is also a biotic, possibly one of the most powerful human biotics alive, and is considered so dangerous that she was kept in cryogenic stasis after she was caught.

History
Born in 2161, Jack was abducted by Cerberus operatives in 2165 from Eden Prime, although it is unknown whether that was her birthplace. Cerberus' motives pertained to her newly discovered biotic potential, a result of accidental exposure to element zero in the womb. As a cover for her abduction, her mother was told that she had died due to complications of her eezo exposure. After initial tests, Jack became the prime subject of a sizable Cerberus experiment on Pragia's Teltin facility, with the goal of enhancing biotic potential in humans, regardless of the cost. The project was a typical Cerberus operation: lavishly funded, highly efficient, and morally indifferent, with a heavy reliance on brutal human experimentation and conditioning techniques in an attempt to maximize results.

Referred to as Subject Zero, Jack was the core of the project, with every successful biotic enhancement applied to her. Many other children of lesser biotic ability were also kept as part of the experiment and treated as expendable lab animals, with many dying in trial runs of treatments to ensure that they would be successful on Zero. Any enhancements that proved lethal were not applied to Jack. She was tortured frequently, both psychologically and physically, in various experiments to test how pain and distress affected her biotic abilities. As she grew in both age and hatred for her captors, her powers eventually advanced to such a level that she became a serious threat to the staff, easily killing one by blasting him into a wall. Kept separate from other children, she grew up believing that the entire world was what she could see outside her window and repeatedly screamed herself hoarse while trying to communicate with others through her soundproofed cell. In reality, the window was a one-way mirror, intended as just another form of psychological torture.

As they were regularly and remorselessly killed in various experiments designed solely to advance Jack's biotic abilities, the other kids grew to despise her as the source of all their suffering. This was only made worse by the fact that (on account of the one-way mirror) the only time they ever saw her was when the staff forced her to fight the other students gladiator-style in order to monitor her biotic progress and condition her to love the act of killing; she would even be injected with narcotic drugs during the fights to further associate killing with euphoria in her mind.

Eventually, while being led to another deadly experiment, the children rioted and attacked the guards. Backed up by their biotics, the riot caused damage to the facility and Zero was freed. At this point her powers had grown so great that nothing could stop her. She would later have difficulty remembering those events for the next years in her life, due to her age at the time and the chaos. She would claim the guards and children attacked her, forcing her to kill them all. When she returned to Teltin, recorded logs rendered it more likely that the children were attempting either to get close to her for safety, since the guards had been ordered to keep Jack alive, or were trying to kill her as a measure of revenge. In either case, Jack's pent-up rage and sudden release from captivity caused her to fly into a fury, killing almost everyone in the facility in a furious biotic rampage before stealing a shuttle and flying off Pragia into the Dakka system, where it was picked up by another ship after several days. Rather than helping her, the crew "used" her before selling her off as a slave.

The Teltin facility on Pragia was shut down by the Illusive Man shortly after Jack's escape. Although operating as an official Cerberus cell and receiving Cerberus funding, years later the Illusive Man would state he was initially unaware of the brutality of Teltin's experiments, claiming that he shut the facility down after finding out it had "gone rogue". This official stance is echoed by Miranda Lawson, who (when confronted by Jack) refuses to admit blame on behalf of Cerberus for Jack's experience, calling her ordeal a "mistake" and blaming it on a splinter group.

After her escape, Subject Zero went on to live a predictably violent and bloody life. In order to sever ties with her past she took on the name Jack, and reacts violently whenever addressed by her former designation. She ran with various gangs, became a pirate, crashed a space station into a hanar moon (becoming wanted for vandalism in the process), and at one point joined a cult, keeping her head shaved even after her departure.

Eventually she was captured and imprisoned in the Blue Suns operated prison ship, Purgatory. During her time there, she was attacked by a group of guards and prisoners who raped her, despite her efforts at fighting back.