F6 is an agent with an unnamed international agency.
The year we first meet this 29-year old woman is 2120, placing her birth around 2090. The world is a considerably different place than we know it seventy years before. Not only has technology changed a lot in that near century but the population has apparently gone through two global wars, the first known as the Wars of Religions and the second called the Eco-Wars. The former seems pretty self-explanatory but the second still puzzles me though their nature is not important to understand outside the concept that they were bad and people remembered them strongly enough to capitalize their names.
When we encounter F6 initially she is going by the name Sienna Madison but remembering that is hardly worth the time since she will, as she is trained since birth to do, discard it as soon as the mission is over. She will not miss it just like she has not missed the many she has used over her years of service or the many she will call herself as we follow her in the several adventures we have of her.
F6 is the name she really thinks of herself as since it is the designation she was given when she was first "adopted" by the agency as an "abandoned ex-utero baby". [Not exactly certain what that means either.] The "F" denotes her sex as female. The "6" refers to her being the 6th female baby so brought into the system. According to her, initially there were more male babies gathered up than females, the males being numbered M1 and up, but it soon became clear to the powers that ran the organization that the females were far quicker to learn the lessons being taught and more capable of surviving the field missions that came later.
Exactly what the agency is about is never fully explained to F6 [or us] except that it is global in scope, multi-governmental in origin, and unknown to all but a few people. The missions pit her against a large number of very unpleasant people, at least one of whom is a war criminal from the Eco-Wars that she is tasked with bringing to justice.
While I/we may not know exactly the details of her job, we definitely learn that she is very good at assuming roles, very good at infiltration, very good at going up against some bad people, and very, very good at survival.