At some point in a tabletop roleplaying game (RPG), the gamemaster (GM) is likely to encounter a useless character. Note: not a useless player (although useless players aren’t unknown, either), a useless character. In this scenario, for one reason or another one of the players has decided to show up for the game with a character that’s wildly unsuited for the campaign. And the player doesn’t want to switch out the character for a new one, for whatever reason.
Now, there’s a standard way to handle this problem: yup, kill the character at the first opportunity and make the player come up with a new one. And this technique works! …But it only works guilt-free if the player was being unreasonable or obnoxious in the first place. I mean, if you deliberately bring an anti-social, brooding skulker to a game solely because you know it’ll just annoy the GM, you probably deserve to have that character nuked within the first half hour. This is pretty close to being a universal truth in the gaming world.
But what if the player isn’t being unreasonable? — Which is another way of saying But what if the GM messed up and didn’t make it clear what kind of campaign s/he was running? Because that’s how it often goes. It’s not really anybody’s fault, in a bad moral/ethical choices sort of way; but if the GM isn’t clear about how his or her game is supposed to go, there’s a chance that a player will design an inappropriate character and then emotionally bond with the character concept. So, how do you as a GM minimize the fallout from that, without being a jerk?
First off: see what’s the exact problem with the character. You might get lucky, and it’s simply a mechanics issue. Those are relatively easy to fix. As a general rule, I would avoid allowing a player have an ability or skill that you flatly don’t want in your game, or are even really dubious about — but if the issue is just that the character doesn’t have the Swimming skill and Amphibious advantage and everybody else in your underwater campaign does, well, just give the character the skill and advantage and tell the rest of the party that they get some free skill points. Nobody at your table will complain, and you should have probably done that to start with anyway.
Problematic characters when it comes to personality and motivations are trickier issues. I don’t have a good answer for the aforementioned anti-social, brooding skulker problem, honestly — but anything that’s less overly dramatic than that could probably be handled by the player explaining why s/he thinks that the character is motivated to participate in the campaign, and by the GM promising to take that into account when designing adventures. If the player can’t come up with a reason, well… that’s pretty diagnostic right there, isn’t it? And it’s become something that the player will himself have to resolve.
Often times, you’ll see people offer advice in these situations like See if you can accommodate the player by tweaking the campaign. I’m going to be a little contrarian here and suggest that you not do that, or at least not to any significant degree. After all, GMs get to have fun, too — and if a GM wants to run an ultra-subtle and clever spy game, having somebody whose character is better suited to do this instead is probably not going to make you happy in the long run. Besides, once you start letting one of the players get to make changes then all the other players will want their turn, too. Which is actually not necessarily a bad thing, but it is a complicated one. Finally, there’s always one option: don’t do anything. Let the player figure out how to keep the character alive long enough to get the experience points necessary to make the character most useful — or, indeed, useful at all. Heck, maybe the inappropriate character problem won’t even be a real issue: a good table can spend a remarkable amount of time roleplaying while never bothering to actually roll any dice. In fact, a good table can spend a remarkable amount of time creatively goofing off and hanging out with each other, which is in itself a reasonably good working definition of ‘having fun.’ In either case, the stuff on the character sheet isn’t necessarily going to be all that much of a big deal anyway, so why sweat it if you get lucky?