So someone asked me in an interview recently if Addie (my MC in Pivot Point) came to me fully formed or if she came little by little. And the answer to that was easy, it's how all my characters come to me: little by little. Some writers like to do a character write up thingy (see, I don't even know what's it's called. That shows you how often I've done it). But I once sat in front of one of those worksheets (ah, there's the word I was looking for--worksheet) staring at those questions (ex. What does your character fear; how would your character react to a horde of bees) That is not an actual question from a worksheet. In case that wasn't obvious. Real questions are much better and helpful.
I figure out how my character reacts when a situation arises. And then I always, always, have to go back and make her/him consistent throughout the book. So at first my characters have a general personality. Like I know if they're shy or loud or crazy or reserved. But the intricacies of their personalities are developed throughout the course of the book. I feel like as long as I can answer those important questions that a worksheet poses by the end of my book, then the character has become.....well, real I guess. (At least to me.) :)
That said, some of my side characters have come to me fully formed. This is probably because I base most of my side characters off of real people in my life. Ha. Just kidding.........or am I? (I am.)
What about you? Do you jump into writing with fully developed characters, complete worksheets, or do you learn about your characters as you write?