Creating Supporting Characters
Novels have a range of supporting characters, and every one of them should be there because they are necessary to tell the story. If a supporting player has no role in the story, then you should consider dropping that character from your novel.
Supporting characters are less important than the main characters, and they require much less planning. Often it's their relationship to the protagonist that defines them.
Some of the typical roles that supporting characters play in novels include:
You will be able to plan for some of these characters in advance. Others will just show up, initially intended to be a minor character or a walk-on. Then they'll act up, or do pirouettes on the page, and you'll find yourself promoting them to supporting status.