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Before starting your story, write as much as you need to feel comfortable with the character. That could be pages and pages, or only a paragraph. (For example, the Harry Potter trio were asked to w...
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#4: Attribution notice removed
Source: https://writers.stackexchange.com/a/8797 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#3: Attribution notice added
Source: https://writers.stackexchange.com/a/8797 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
Before starting your story, write as much as you need to feel comfortable with the character. That could be pages and pages, or only a paragraph. (For example, the Harry Potter trio were asked to write up something in the voice of their characters. Radcliffe did a page, Watson did 20, and Grint did nothing. When asked why, he said, "Ron would never turn in such an assignment." The director was like, "Yep, you totally understand Ron.") If your first one is "over the top," then don't write the others so long. Or alternatively, go ahead; why not? Who cares if you write 50 pages of stuff only for you, if you decide you need it? As you go along, keep checking back with your notes, and add, remove, or edit as needed. If some character trait is crucial to the plot (he's afraid of fire because his brother burned him as a child, she was inspired by her grandmother to be a singer no matter what the cost), then you need to iron that out first, and stick to it. As far as "my characters evolve out of character," either you need to be more disciplined and stick with the character you created, or you have to change your plot (and therefore your character bio) to accommodate the new information.