I don't know how other storytellers work, but I know for sure that I do not invent my characters. Basically, it happens like this:
A glimpse of a character appears in my head.
It soon occupies all my being.
It starts hanging wallpapers and decorating its new home in my head.
It starts talking to me.
Tells me a little about their habits.
Their hair colour.
It shares something weird that doesn't make sense.
A few months/years later I understand what it all meant.
It makes me draw its portraits.
It comes to my dreams.
It reminds me of something in myself.
Makes me wonder about other people.
Makes me do some research.
Demands that I start writing its scenes.
Gets annoyed when I write about someone else.
Gets annoyed that I write very slowly.
Shouts that it's been in my head for years and wants to get to other people's heads now.
So that it can hang wallpapers and decorate everything there as well.
Can You Hear Them?
by Ozzy Osbourne