Every story has Main Characters, Secondary Characters and then those Other Characters, who have names and enough bits and pieces to make them interesting but aren't as three dimensional as a Main or Secondary. They aren't meant to be.
They exist, from a writer's perspective, to make your world interesting and sometimes give the Main and Secondary Characters someone to interact with aside from each other, or to be sources of amusement or animosity or information. Other Characters serve these vital functions, but aren't designed to be front and center.
However, every writer knows that sometimes characters have a mind of their own and decide they are going to be more important than you planned.
The third book in my Adelheid series is due out this summer. I had written this story once before some years ago, but decided to rewrite and revise to put it in the Adelheid series, but several of the characters are the same. One of the background characters -- an Other Character -- was a bartender named Quintus.
Quintus came a little more to the forefront in this version of "Voracious" and he even made a cameo in the second Adelheid story. He's a very old (600+ years) vampire who owns a vampire bar named 5, and he gave Dakota some information in "When Forever Died" and he's more pivotal as D's friend in "Voracious."
Aside from name, age/species and career, I only knew that he was huge (6'6" at least and nearly as wide) and had very dark skin. I had the basic idea of what he looked like and his personality, but just enough to write him.
However, as I wrote book three, he decided he wanted to be more and started becoming a lot more interesting. He's started showing his history to me, even though I didn't ask for it! He is starting to tell me an intriguing back story involving his parentage and early life in ancient Rome. He has even given himself a back story connection to another character that is in "Voracious" that I had never planned to tie him to!
He is, in fact, making himself so interesting that he might end up getting his own story, whether a short story, novella or novel, I don't know but it looks like he's going to get his chance to shine, despite all attempts to make him just an Other Character.
This is a cautionary tale to all writers who think they are creating background characters, because they don't always listen to what you tell them and stay in their place. Sometimes, they decide that they have much more complex and rich backgrounds than you thought, enough that they demand a story about them. So all writers beware of those Other Characters that might just stage a mutiny on you, like Quintus has done to me!
To see more of Quintus check out Mia's Adelheid series on Amazon.