It is often a good idea to have a background story in mind for characters. It doesn't (and generally shouldn't) all be in the finished story. That said, it makes the character more complete and provides a rationale for their actions.
Cynthia (nicknamed the invincible).
Born 2300 +- on Beta Cygnus 8 (her planet has a different period than Earth so the exact year and date are problematic. She can give her birthday in the local calendar). She doesn't have a last name, but does have an identity number.
Recruited at an early age (biologically about 12-13) to the academy to be a spacer. This sounds like an honor, but it isn't. It means she is bright but doesn't conform to societal norms. In other words she is 'surplus to requirements'. She is trained with a number of males and females of about the same age. In order for them to stay sane during long solo missions in space they are given a drug cocktail. Part of the cocktail preserves their youth, and part damps emotions.
They're let loose on the Galaxy to expand Terran space. Each starts with a relatively inexpensive (10,000-100,000 credits?) scout ship. This is much cheaper and more effective than trying to use an army or navy to conquer space. If they survive long enough to pay it off, they're free to go about on their own. (Hope this doesn't sound too much like a video game). Her class is about 1000, 60 years later there may be 10 left. One is "one eye Pete" who is on exhibit in a Cataxi zoo.
This means she's not really a fully functional human. She's a damned good space pirate/privateer, and has what she considers a reasonable amount of credits stored on her ship. (It's not much - the Terran empire charges steeply for fuel and food). She will take what she wants and is well conversed in methods of scams and petty crime.
She develops an unhealthy interest in 'virtual men' in the AR games unit. She hasn't met many real men, and the other spacers are rather emotionally stunted. It tends to lead to rather awkward encounters, where even if they make love, they don't. She's also had some encounters with one alien race; the Xylub who are both utterly untrustworthy and sex-mad (They see it as a religious experience).
Her computer companion, which exists to keep her healthy, has decided she needs to take a break. (Also if she doesn't go off the drugs for a bit and soon, then she will never be able to stop them. It may not sound like a bad thing to be young forever, but if she misses a dose after that threshold she's dead.) He's a bit of a matchmaker, which she does not approve. He takes advantage of an accident to let her loose in Regency England Her favorite AR game is 'Jane Austen World', where she is trying to seduce Darcy. She finds reality a bit daunting and not quite as much fun as the game.
She's rather foul mouthed, and impulsive. The conditioning before she's dropped off will remove the foul mouth (She'll still think the words, just can't say them. Unless she's really really really upset, and even then they are watered down.) She finds she's capable of friendship and human attachment. This is essentially a new experience for her. Her parents, if they were alive, just dumped her on the academy. She has no desire to visit home or family.