Most novels and narrative non-fiction will have characters/people who aren’t main characters. If you’re creating a video game, then you might need to know a lot about these characters to let players interact with them, but for narration the needs are much simpler. Here’s how I create them.

First, I need to know what role they play. This is typically minor. Let’s say a main character needs to take a taxi. They’ll need a taxi driver. So what should this taxi driver be like?

I’ve known some authors who roll dice to decide, literally leaving it up to chance. That can be good fun for gaming, but I prefer to more deliberately decide. In general, I choose a few characteristics that make the book more true-to-life and work from there.

True-to-life doesn’t mean stereotypical. If my hypothetical taxi driver is an immigrant, then I’ll need to work to make sure I’m not playing into stereotypes–positive or negative–about how many taxi drivers are immigrants. Is the driver male, female, non-binary, or agender?

Note that this isn’t about working in as much diversity as possible. A cishet main character might not even notice that their taxi driver is agender, and readers won’t know unless you tell them. This can provide impetus for a conversation that reveals more about the main character’s morals, motives, thoughts, etc.

If all of your background characters look and think like your main characters do, that’s noteworthy, too. Whether that’s what you intend as an author is something only you know, but even homogeneity can be a point of revelation and tone for your novel.

Every background character is the protagonist of their own novel in some alternate universe. (Or maybe even in this one, if you write in a series.) Give them a story, and then let pieces of that story be seen through your main characters.