Some of my characters I've had for so long I don't even remember where or how they came about. Others I can trace back to one definite decision to create the character, or in some cases one conversation that brought the character about.
The easiest examples to use are characters for my as-yet untitled WIP trilogy. One character in particular, Antonio, has been rattling around my head since the fourth grade. Over the years, he's spawned his own parents, an uncle, two older brothers, and a host of information both plot-relevant and completely random information. One thing I will say though, and this is one of my personal golden rules of writing:
No characterization is wasted.
This rule will definitely be visited more in-depth in a future post, but let me clarify further: no matter how useless you think a bit of information you have about a character is, put it somewhere. If you can remember it, tuck it away in your mental files. If you can't, write it down. I try to keep files on each character I have (either in a word document or in my writing program WriteItNow4, which is the topic of another upcoming post), and I write down any tidbit I can. Will most of them be used in the novel? No. It's probably never going to be relevant to the plot that, for example, Miguel (Antonio's older brother) is allergic to strawberries? Probably not. But it will change how he interacts with the environment around him, and how other characters, especially his family, interact with him. It may be mentioned in the actual story sometime - who knows what he'll decide to talk about - but even if it isn't, I know it, and the characters know it, and that adds another layer to the never-ending onion that is a good story and good characters.
Characters can come from anywhere. I remember creating an antagonist for my current WIP, and at the time I was on the phone with a former friend. I was struggling to name the character, to which she responded, "It should start with a D. Villain names start with D's." Her words, not mine. Her reasoning behind this was, at the time, she was reading the Gone series by Michael Grant, where one antagonist is named Drake. She also suggested the name Damien, which was at the time the name of a teacher at my school who I doubted would appreciate having an antagonist named after him. I, eventually, settled on the name Dmitri. What started out as the quintessential "school bully" antagonist with a twist, evolved into a (if I may say so myself) very complex and multi-faceted character. He actually was more of the catalyst for Miguel's appearance than Antonio was; somehow, he decided he didn't want to be a jerk on his own; he needed a "posse" for that. Somehow, Miguel grew from that, latched onto Antonio as his brother, and then produced a twin for himself. Eventually, an entire cast of characters found their way into the story, and Bob's your uncle, as they say (I don't know if anyone even really says that, I just like it).
I can't find the exact place where I read this anymore (if someone can, please feel free to Tweet it to me), but JK Rowling once said (paraphrasing of course) that Harry Potter "waltzed into (her) head one day, fully formed". For many characters of mine, something very similar has happened. But, like I mentioned earlier, sometimes it's a lot of work. I'm not sure I'd call it building a character, because I think oftentimes characters come fully built; it's just a matter of putting the pieces in the right places. The analogy I'd like to use, because it sounds cool and science-y, is unearthing a fossil. You start by hacking away the big bits with a pickaxe or something similar, but eventually it comes down to being on your hands and knees with a little brush, dusting away the tiniest, most insignificant bits. That analogy doesn't really work, though, nor is it very relatable. In terms of starting with large pieces and moving to little ones, it does, but I think a better one would be that creating a character is like putting together one of those complex Lego sets. You start off with the big base pieces, and then your put together smaller pieces, and stick those onto the bigger pieces in the right spots. Then, if you've done it right, you'll end up with something you never would've guessed would come from those little plastic bricks and fiddly little bits that go all over the floor and thank God they give you extra because how do I keep track of all of these and - I'm rambling again.
I think this is a good place to finish off - with that image. Character building starts off with the big pieces - What's their name? Why are they in the story? What's their goal? and goes to the small - the little things that make a character seem human, rather than just words on a page. Those little pieces, those details, like Legos, turn a boring piece of plastic into something cool and fun to play with, and turn a flat, forgettable character into one who will worm their way into your readers' hearts and make them come back to your books time and again.
