A character’s backstory – all the stuff that happened to them prior to the start of the novel – starts with the highs, lows, traumas, and major life events of the character’s past. This is the stuff that has shaped the character’s personality – what they want, how they go about getting it, what they avoid, and so on. It doesn’t actually matter whether the backstory is real history, stuff that the writer made up just for this book, or events that happened in the previous eight books of the series when the writer is working on Book 9. What’s important to this story are the cultural details and life events that make them act the way they do, and it’s what got each of them to whatever place they’re at (physically, mentally, and emotionally) when the story opens.
Because backstory is integral to character’s personality, it is generally most effective to handle it the same way the other elements of characterization are handled – bit by bit. For a pantser, this often happens naturally, because they’re getting to know their characters (and their characters’ backstory) as they write; the trick here is to keep a sharp eye on what your characters are doing and saying and realizing what it implies about their personal history and culture. For planners (or those working on the eighth book of a series), the focus is on sorting through what you know about your characters’ past, deciding which things the reader needs to know to understand the character’s actions in this book, and then figuring out where it goes and how to convey it.
In real life, we get to know people a little at a time. Readers can get to know characters (and learn their backstory) in the same gradual way. Since this is how it works in real life, it usually feels natural, which makes the novel more believable. It also makes the backstory easier for readers to remember, since they’re getting it a little at a time, just as they’re getting curious about the character. Stringing out a particular bit of backstory may be critical to the plot, as in any story where the climax involves the revelation of a long-held secret. The thing to remember here is that the more you tease the reader and the longer it takes to get to the revelation, the more important to the story the backstory has to be. If the Big Secret turns out to be that the dentist’s daughter has a sweet tooth, the reader is likely to be disappointed (unless that’s the final clue that pins the murder on her).
It is possible to provide a three-page backstory infodump each time a new character is introduced, and this was a fairly common technique in the 1800s. Nowadays, repeated infodumps can make a story feel dated (though if you’re doing a pastiche of an 18th or 19th century novel, it might be just the thing), and they also need to be really fascinating or a modern reader may get bored and start skimming. One key to making a characterization/backstory infodump fascinating is to remember that all the information and presentation has to be interesting and intriguing to someone who does not yet care about the character. Writers usually do care, often quite a lot, before they ever present a character for the first time; readers are just meeting them, and don’t have any reason to be interested in the subtle details of the character’s fountain pen collection that the writer thinks is so important and interesting.
Infodumps aside, backstory and characterization come out gradually through context, in the character’s actions and reactions, in conversation as casual asides or long explanations, and in the viewpoint character’s thoughts and conclusions (which may or may not be reliable). It’s a lot easier to get backstory in for most POV characters. If a POV character sees potato salad on the buffet and suddenly feels sick to his stomach, the writer can immediately put in an explanation or a hint (“He hadn’t been able to stand potato salad since his stint as food-taster for the king. Six attempted poisonings had been enough…”). If the POV sees some other character take one look at the buffet and go green, he can wonder what’s up with that, and if he’s curious enough he can ask someone else, but unless he already knows that Mavis nearly died of potato-salad-poisoning, he can’t explain to the reader what is behind the reaction.
A certain amount of backstory can be provided by implication, without needing to be stated directly. If the first thing one character says to another is “’owdy, gov’nor; what’ll it be today, stout or lager?” we tend to make assumptions about that character’s background, class status, and job. As long as the next line isn’t something like, “You can’t fake a British accent worth a nickel, Greg, and I know for a fact that all you have in your fridge is Diet Coke,” the reader will take those initial assumptions as correct. Misleading the reader like this can be useful, but the longer the story goes on before the misconception is corrected, the grumpier the reader is likely to be about it. In extreme cases, readers will insist that their initial interpretation was correct no matter what the writer thinks or says.
This is something I struggled with in my first novel. Characters A and B react very differently to the same information, and it’s largely due to their backstories. A gives a little insight into B in conversation with another character — which I still worry seems forced, but I don’t have a better idea — but A’s history is largely opaque to the reader. She’s the POV character, but she’s thoroughly rejected her background and doesn’t tend to dwell on it, and she’s not much for talking about herself anyway. Which leaves me stumped for how to work it in, and hoping the reader can extrapolate in the right general direction from some very tiny hints.
How would it affect the plot if someone from her past showed up?
It would have to be some other book entirely.
Characters who have a mysterious backstory can be intriguing; think of all the stories where a big part of the climax is the revelation of some emotional backstory that explains a bunch about one or more characters. As long as you drop intriguing hints that let the reader know there is backstory (and that the author knows it and will reveal it in due time), it can be a feature.
If you don’t think whatever-it-is is dramatic enough for a reveal, or if it really doesn’t apply in this story, see if you can make one of the existing characters either a nosy parker, or just puzzled enough by the different reactions to ask what gives. Since you’re in A’s head, she can say “None of your business” and still let the reader in on the stuff she’s just been forced to remember.
Depending on the sort of backstory, there may also be occasions in which knowledge A learned during her now-rejected background is useful or even vital, which will give more clues. If she knows more about court manners than a caravan guard should (or more about caravans than a court dandy should), or way more about poisons and antidotes than anyone should, it lets the reader know there’s something going on, even if she absolutely refuses to talk about where and how she learned it.
It’s definitely not dramatic-reveal material. In broad strokes, A grew up on what amounts to a commune, whereas B is third-generation loyal government service. So when the organization they both work for (which makes the NSA look open and sharing) pushes a dodgy agenda, A is far more ready to see the ugly underbelly, while B is determined to put the best possible spin on it for as long as he can.
It’s not at all a mysterious backstory in the traditional sense, but it does explain how A & B can look at the same information and come to very different conclusions, without either of them being stupid or evil.
I suppose I might be able to wedge a little inside-A’s-head info into that already-forced conversation where B’s background is mentioned. It doesn’t feel right for A — she’s not hiding from her past, she’s just made a life that it’s irrelevant to — but it might help keep the reader from thinking B’s an idiot for not seeing what’s going on at the same time A does. Which is a thing I worry about.
It sounds as if you want the reader to agree with A that there’s a dark underside to what’s going on. That means you don’t really need to explain A’s backstory in detail; what you want is to explain why B is determined to put a good spin on the same info. Possibly the simplest way is to have them argue about it directly, with B saying things like “Look, my aunt worked for that division when I was a kid; they wouldn’t DO that” and A things like “That was thirty years ago! Things have changed.”
If they’re not at the direct-argument stage, see if there are places where B’s comfort with government bureacracy and A’s suspicion of it can be highlighted in other ways. Maybe early on A comments negatively about the mystery meat in the cafeteria, and B rolls his eyes and says, “It’s probably budget cuts. Not everything is a conspiracy, you know!” Something minor that ISN’T connected with the main plot.
I may have that angle covered. If there’s one thing those two can do, it’s argue! 😉
I think that leaving the backstory unexplained until it’s absolutely necessary can sometimes clash with a first-person or tight third-person narration: if we’re reading X’s thoughts, and X knows something important that colours their impressions of what’s going on, but the story doesn’t mention it, it can come out feeling like a bit of a cheat.
(This is close kin to the “narrator did it” type of murder mystery, and starts shading into unreliable narrators in general, but that’s a different argument.)