Several of the gurus who have come out with story theories have also suggested archetypes that are found in stories. You may have started with four basic characters: hero, enemy, friend and mentor but you may find looking at these characters useful.
Christopher Booker’s archetypes
Good old man
Innocent young girl
Rival or “shadow”
Joseph Campbell’s archetypes
Christopher Vogler’s archetypes
Vladimir Propp’s archetypes
Other fairy-tale familiars (as found by the brothers Grimm)
The Guileless Fool
The Meddlesome Fairy
The Wicked Crone
The Charming Prince
The Beautiful Damsel
As you will see, there is a lot of overlap between the different gurus. I haven’t gone into a lot of explanation here; let them be what their name suggests. If you are really interested in archetypes you may like to look at Jung and also the work of Carol Pearson and Margaret Mark: https://en.wikipedia.org/wiki/Archetype
Why work with archetypes?
They can give each of your characters a function within the story. It’s important to ask why characters are there at all and this may be especially important for minor characters. And readers love archetypes, even if they can’t name them. They recognise them as familiar.
Use a work in progress and see if you can fit one of these characters in or build up one that you already have to become one of them. Can you pinpoint the role of any other characters you have there? Or maybe in something you’re currently reading?