Did they spring fully-formed from your forehead like Athena from Zeus? Or did you need to get to know them at some point? I suspect for a lot of people, it’s the latter. And I think a lot of discussion in this thread is about the different techniques and approaches people have for doing that.
You know, some of them did! I've tried to describe my creative style to some people. Best i can say is that i dont write at all, i dont create at all, i channel this stuff. Where it comes from i have no idea. I need a character, lets say a female love-interest, and she's there. Boom. I need a minion for a malevolent antagonist, he's there. I need details, she provides. I need more, i just wait... more comes. They are all completely from the ether, and often i'm even shocked as to why they come that way. Occasionally i'll nix a certain trait, or explanation, but i'll still wait for the character to replace it on their own. Its hard to explain. Its like i',m not writing/creating at all... i'm taking dictation. Other times i'll just 'grab' a character from somewhere. I'll turn my tattooed tough guy friend into a misunderstood beta teen. I'll turn an 8yr old Cosby-kid into a hardened USMC mercenary. I'll turn a sappy Hallmark movie lead into a vicious LotR style elf. With the 'grab' technique i can have staggering amounts of backstory, character, or motivation. I love to twist things...
Sometimes, for me it can get truly intense, as even plot twists and endings reveal themselves. I've had stories move themselves along so effortlessly sometimes i kinda get to sit back and read, like reading my own book for the first time. Problem with that is, i think its also made me a bit lazy.
There are a couple of characters in my current novel whom I am still struggling to fully understand after working on the thing for more than two years. And understanding them doesn’t just mean knowing what they like to put on a sandwich. It means knowing how they would respond to any situation, what desires - conscious or unconscious - drive the choices they make. It also means shaping them coherently so that it makes sense when they do the things I want to have happen in the story. And it means figuring out how to reveal those details of characterization within the weave of the story itself. That’s a lot to do and it doesn’t happen in an instant.
For me, it’s very helpful to place my characters in situations other than the ones that appear in the novel, and probe their responses to those situations.
You know what reading this last paragraph brought to mind? Some scene in a movie somewhere, i think a kid who's recently lost her mom telling her dad that she cant remember her face. Her dad says: 'dont try and picture her face, or remember faces at all, instead, remember something that happened, a time you had with them... and the faces will come to you'. Or something like that. Thats actually really good advice, and it works. So taking your character and say, 'dumping' them into a scene that requires, or creates character might just work. I actually do a lot of 'deleted scenes' writing... chapters i dont intend to publish. Some can be pretty silly. Like, big tough badass goes to a jewelry store to buy his girlfriend a necklace. Or strong female lead goes on a date with some asshat narcissist. Or just grocery shopping during a robbery or something. You'd be surprised what comes out of the woodwork, or what you might learn from the scene. I'll write alternate endings too, 'it was just a dream' endings, etc, etc. I do a lot of different things to really squeeze blood from stone (my characters). Sometimes i'll even get a story chapter out of it.