In any long form work, there will be minor characters who emerge from the underlying quantum foam, serve some function in the plot, then sink back, never to be heard from again. These are not the unnamed people who populate a novel. These background actors might interact with your major and minor characters, and might be the cab driver, the barista, the receptionist. They might be completely faceless, like the members of the orc army or the majority of the other students at Hogwarts. These characters are fine in their place.
But what about the walk-ons? Some characters walk on, have one scene in which they get fleshed out a bit, then disappear. They fill in a chunk of backstory, or give your MC a chance to show how nice he or she is (or how cruel). The role they play is important, but it seems a bit clumsy to give someone a single scene. Especially if you have a couple of these characters, it can make your novel look like a scattershot mob scene.
One strategy is to combine these walk-on parts and make them into full-fledged minor characters. As they come and go through the novel, they can still serve their original purposes of driving the plot, revealing information, and providing motivations or emotional mirrors.
A complication arises when the walk-ons are very different. I recently combined a couple of characters in order to solve the same problem they each had: a couple of clumsy stereotypes with not enough to do.
Character 1. A large, Caucasian, male postdoc, a gamer and geek fanboi, socially inept, the kind who goes to Comic-Con and wears “Gordon Freeman Lives” T-shirts.
Character 2. A small, Asian, woman grad student, shy and hard-working, the kind who spends all her time in the lab or writing science journal articles, and knows more about isomer decay rates than about “Call Me Maybe”.
They each had one scene, in which they revealed some backstory (Character 1) or set up some foreshadowing (Character 2). Later in the book, the reader is asked to care about these two, to be worried as to their life or death. But really, who cares? The reader doesn’t see either of them long enough to develop any emotional investment in their fates. Besides, they’re so generic, it’s not easy to find anything to latch onto.
Now, consider what happens when I combine them.
Fusion character. An Asian woman postdoc of medium height, normally social in the lab but bubbly and enthusiastic when talking about video games, hard-working and a productive scientist, but wears “Gordon Freeman Lives” T-shirts under her lab coat and goes to Comic-Cons.
She’s much more interesting, isn’t she? There’s much less of the stereotype in her, and much more of an interesting, multifaceted character. It’s almost like we’ve given her a life of her own, a personality that exists outside the scope of the needs of the story. In her first scene, she helps reveal some backstory. Later, she sets up some foreshadowing. By the time her life is in put in danger, we’ve had a number of scenes to get to know her. We CARE about her. It MATTERS if the hero will be able to go save her in time.
True, reworking the scenes to make these walk-ons into one person instead of two (or more) people takes some effort and attention to detail. In my case, sniffing out every “he said” and revising them to “she said”, and so on. Tedious, but worth it.