Katy "K.C." Cooper is an agent with the Organization.
That is the only name I have heard for the intelligence agency that she joins in the first recorded adventure. It likely, of course, has a better one but that is what her parents call it and they have been with it quite a long time so that is what she calls it, ergo what we call it.
Cooper is new to the group because she is pretty new to everything, she being a 16-year-old high school teenager. Before the events of that first mission, she had no idea that the Organization existed, that her parents had been operatives for it for more than her entire life, and that she had been practically groomed for membership from infancy.
Cooper is an African-American girl. I would call her a "normal" teenager except that she is quite a far distance from being "normal" in that she is not only a math genius, she has also been a prodigy at gymnastics and at martial arts, having been taking lessons in both since she was old enough to walk.
Her parents are Kira (her mom) and Craig (her dad) and we learn very little about them other than they are agents and have been living with cover jobs for years. They finally reveal their true vocations to Cooper when the time was right and the need for her skills arrived.
As expected, once she learns the truth, she is a bit stunned. As not so expected, she is both nervous as heck and super-gung-ho. Her biggest disappointment is she cannot tell her best friend forever, Marisa, the truth which causes a few problems since much of her missions will find that girl innocently in the mix somewhere. [Note: in the wiki devoted to this series, she is described as the 'deuteragonist', or "the person second in importance to the protagonist in a drama". I learned a new word!]
Cooper has a younger brother, Ernie, who is quite a nerd and socially inept and totally in the dark about the espionage activities of his sister and parents, at least for a while.
She also gets an "11-year old sister" named Judy. That relationship is put in quotes because Judy is an android created specifically to join the family and assist on missions.