Luckily, there's a simple answer that works at least nine-tenths of the way, giving you both a backstory and the ability to remain flexible. Rather than laying out your entire story before you start playing, you make use of something I like to think of as progressive backstory. (You can also call it too-lazy-to-finish-making-a-character backstory if used during a pen-and-paper setting, but the other way is a little catchier.) The idea is that your character doesn't start out with a backstory so much as the suggestion of one -- as the story comes up, it gets written.
The easiest way to start is to just make a little text file with, at most, a three-sentence biography. Anything that starts going beyond that is probably trouble, and anything that starts to mention a large number of NPCs is probably big trouble. (Remember, the game is going to have its own ideas about who your character's lifelong enemies ought to be, unless you're in Champions Online.) It's enough to know the loosest picture of who the character is but broad enough that you can fill in a lot of details later -- much like the picture you get of most characters at the beginning of a TV series.
By way of example, I'm going to use a character I'm playing in City of Heroes, since she's still young enough that her earlier days are fresh in my mind. Gravelines started out with a very simple biography: she was a rich girl without much in the way of brains, so she wound up joining Arachnos as a soldier when the money started to run out. Coincidentally, she's turned out to have something of a talent for it. She's an airhead with a rifle and no real sense of the value of money.
That was all she started out with. However, as I got her involved in a villain group and played her more, other pieces of information started coming to light. A fellow member asked for volunteers for newspaper missions, so I went along -- and the first one placed us smack-dab in the middle of a Crey facility. On the spot, I decided that she thought Crey was super awesome, and added a little line to her backstory: she always wanted to work for them and applied out of high school, but she got passed over. It hasn't come up much since then, but it made for some entertaining mid-mission roleplay as she gawked and cooed at things needlessly.
As I was writing her dialogue with other people, I realized that she needed friends to tell stories about. Not only did I add how she was a social butterfly outside of her main job (as a soldier for Arachnos), she began name-dropping her friends endlessly. I haven't detailed how she met any of them, but I have gone into details about each story that she's told -- which helps me bring some things up more than once, only to have her cut short as she's reminded of the fact that she's told the story before.
On a whole, Gravelines now is fairly fleshed out -- she has old friends, casual friends, hobbies, family relationships, and a slowly-growing distaste for regular parts of her job. Rather than starting from a finished state, I added bits and pieces via play in order to help make the whole thing feel organic -- and ensure that the stuff in her backstory was relevant to what was going on, since it wouldn't be included unless the situation warranted it.
There are two potential pitfalls to this system, both of which might be obvious. (But humor me.) You could run into a situation where you start deciding everything your character does triggers some childhood memory or another, and your character starts to sound less like a real person and more like Kup or Grandpa Simpson. ("Back in my day, we didn't have the Skulls, we had the Thighbones! Of course, actual thighbones were rationed on account of the war, so we had to make do with wooden replacements...") On the flip side, you could also just keep passing over every opportunity to flesh out your backstory, at which point it becomes increasingly obvious that you're hanging a loose suggestion of a person on three tent pegs.
So where's a good example of this kind of character building? Lost.
Okay, okay, I freely admit that I have a tendency to call on the show whenever it suits my purposes. But if you belong to the camp that adamantly believes the whole show was being made up as it went, you have to admit that the flashback sequences were masterful ways of disguising it. Everyone's past is kept vague enough through the start of the series that as flashbacks reveal new things, it fits in with pre-established events.
And the show struck a decent balance. Main characters weren't constantly having strings of episodes focusing on their past -- but every few episodes, they'd get another story that fleshed them out. It was spread out just far enough that by the time they focused in again, you had time for prior stories to sink into your head. Over time, people turned from ciphers into well-detailed individuals. That's what you want to go for as you're building backstory -- just slow and periodic callbacks to a character's younger days based on the situation.
It's a subtle art, but it winds up creating some very invested individuals. And it ensures that you never miss out on that moment that would trigger a memory. When you do it right, no one even notices that you're doing it on the fly.
That's our dose of roleplaying thoughts for the week. Questions? Comments? Hateful diatribes on the subject of making things up as you go? Send them along to Eliot at Massively dot com, or leave them in the comments. Our next column will either be on backstory NPCs or on the integration between characters and abilities, depending upon which seems more interesting and if there are arguments made strongly for one or the other. See you next week!