Gabriella, the Mantis, is a refugee from the KGB.
She is not an agent though that is not from a lack of trying on their part.
We get a horrific glimpse of her dystopian life eleven years before the first main adventure, a time when she was 10 years old and lived in little more than a cell from the time her KGB operative parents died in action when she was a year old. The KGB took control of her and used the opportunity to train her to be the ultimate killing machine. "She has been commanded to kill a number of things, and has done so without hesitation." Her abilities with weapons, such as guns and knives, was impressive and her fighting skills were astonishing for someone of her age. She had been taught from the beginning to have no fear - or if she did have some, to never let it control her.
It was during a forced examination to which she vehemently objected that she saw an opportunity to escape, severely injuring with just her martial arts skills several large guards, disappearing into a world she had never seen before except in pictures and film clips her instructors had chosen for her to see. "A glazed look fell over her eyes as she assessed each thing that she passed by. The shop windows, the people walking on the street, and even the street lights she had never witnessed in person. Those images had come through photographs, books, and television. Her world had consisted of the underground lab that held her for her training, and it kept her encapsulated from everything in the world other than what they wanted her to see."
Breaking into a department store deep in the night she gathered all the things she thought she would need, from clothing to blankets, food to firearms, ways of starting campfires and a hammock on which to sleep off the frozen ground. The training they had pounded into her daily came in very handy for deciding on such things, despite her still young age. Gabriella was determined to survive and that is what she did. The KGB which had created her was just as determined to get her back to either restore her obedience or destroy her.
She has the nickname of the Mantis, though she often enough asserts she is not the one so named, because that is a term used for a woman who has been very active in going after people or organizations which has been abusing those less fortunate and have been able to get away with it because they either have the power or know those who do. Considering the forceful way she handles the bad guys, it is no wonder the full name for this mysterious person is the Fighting Mantis.