To make all of our lives (but especially mine) easier, we're going to assume that you are modeling your character after someone specific, a character everyone here is likely familiar with. Since my editors have threatened to force me back into the box if I mention Transformers or Lost again, we'll go with an easy standby -- Batman. We all know who Batman is, right? Parents gunned down in alley, fighting criminals, and so forth? Great.
You are not Batman
The first thing to observe is the simplest: You are playing a character based upon Batman. You are not actually playing Bruce Wayne. Your parents might have been murdered when you were a child, but it was not in Gotham City, and you are not the heir to the Wayne family fortune. Even if you are playing in a game where cross-dimensional travel is pretty common, you are still not the original article.
Why? Because even leaving aside obvious copyright issues, and even if we assume Batman makes some amount of sense in context (a City of Heroes scrapper maybe; a World of Warcraft warlock not so much), you're trying to create a character inspired by a fictional individual. You want this to be your character, not someone else's character you're taking for a spin. And the copyright/context issues are there, to boot.
Boil down to the essence
The problem with porting most fictional characters into a roleplaying setting is that in most fiction, the characters are depicted as being either at or near their full potential. Early Batman stories, to continue our example, depict Batman as already having mastered several dozen martial arts as well as having an arsenal of gadgets and a knack for forensic analysis. We certainly don't see Batman starting out being easily mobbed by a half-dozen thugs for the first several parts of his career... but that's what an MMO demands of its characters.
But odds are that the reason you want to play Batman isn't because he can kick everyone around without breaking a sweat (there are plenty of other games that support that well enough). It's because something about Batman-the-character is appealing to you on a personal level. So strip out everything else from Batman -- get at the core of what makes him interesting to you.
Without all of the window-dressing, Batman can be boiled down pretty simply: He watched his parents die in front of him, then swore revenge on all members of the responsible group (criminals, in this case). He spent a great deal of time training, then started waging a one-man war on his sworn enemies from the shadows, all the while succeeding due to a great deal of natural skill and talent.
Certainly you can change the details, keep him from being a direct rip-off of Batman. Maybe he didn't watch both of his parents die, or maybe he swore that he would be strong enough to survive instead of swearing revenge. The important part is that when you remove everything but the most basic elements of the character, you can find which part of the character interests you for your own purposes. That leaves you free to start making the changes you need for the character to become your own rather than a generic export.
Change the specifics
You know the core of what makes the character so interesting to you now; that means it's time to start working them into the world. In this case, we're going to assume that the part that interests you the most is the idea that Batman is waging a silent war from the shadows, the only cop on the crime planet as it were. And we're going to assume that you're not playing a superheroic game, so you have to come up with something a little more specific than "crime" for your character to fight.
This is where you start baking the character further into the game world and distancing him more from the source. In order for this particular concept to work, you need a group of enemies that are generally not seen as a major threat to anyone else. Your character could be on a lonely crusade against that group, which might explain why he's such a small threat when he starts out in the game. The other possibility is that your character is fighting something that's a definite threat, one against which a lone individual seems ill-suited -- the Fomors in Final Fantasy XI, the Dominion in Star Trek Online, the Dark Riders in World of Warcraft.
You're left with some of the traits that you started with, but a lot of them are lost in the process. But you still capture the elements that attracted you to Batman in the first place -- he's stark and isolated, with an understanding of how impossible his task is and no option to give it up. There's nothing there that screams your character is meant as a riff on Batman, but you can still see the roots under the skin. And of course, if someone asks you, you can always tell him that was where you started.
That's our look at character imports for this week. I'm interested to know what you think, as always, so feel free to mail me at firstname.lastname@example.org or just leave a comment after the article. Next week is going to be interesting, as I have two different ideas that might come to fruition depending on the events of the weekend. You'll just have to come back and see.
Every Friday, Eliot Lefebvre fills a column up with excellent advice on investing money, writing award-winning novels, and being elected to public office. Then he removes all of that, and you're left with Storyboard, which focuses on roleplaying in MMOs. It won't help you get elected, but it will help you pretend you did.