When I read a novel, I like to know a few things about the principal characters, say a character profile, not a Doris Kearns Goodwin biography. So I feel it's only fair that when I write I provide a decent amount of background on the central characters. Figures of mystery bore me. They also make me wonder about a writer's ability to create characters you might recognize if you bumped into them at the opening of a play or at your child's playground.
So if you're going to provide some biographical info, a/k/a backstory, on a character, when is a good time to do it? Not in the middle of an action sequence: We interrupt this fight to the death to bring you a Hallmark moment. Not good. It's also not wise to front-load a life story, at least in popular fiction, because you want the plot to carry the reader into at least the second chapter and probably farther. Withholding a character's personal details until the last moment smacks of a Morris the Explainer ending where somebody has to make clear what's been going on. Very clunky technique.
So what does that leave? Yes, the great middle. Ideally the point at which we get to know someone should be dictated by story logic. That is, some action should take place that makes the reader ask: Hey, why'd he, she, they do that? The biographical info that follows should answer the question. It's still Morris the Explainer, but he's a much more welcome guest if he arrives in the middle of the party rather than early or late.
That's the way I feel, anyhow. And that's what I did today, wrote five-plus pages filling in the blanks on who three of the story's antagonists are and why they act the way they do.
Day 34 of writing my new novel is done.