What is the character, genre, and setting.
There are plenty of 20 questions type lists. Those are a good place to start. Shadowrun has a good set up to 3rd, I assume WizKids/FanPro/(not FASA) kept it for the newer editions.
When it comes to fitting background themes to setting, this is where the GM has to work. "My character grew up raising and training the best warhorses in the land. That's what his house does. See? I even maxed out my ridin' and horse trainin' skills. And my dude's like 6 feet tall and green eyed and he's got a wicked tan but he's normally really pale if he can't work on it. And he trained the horses by the sea, that's how he got the awesome tan. So, does he fit the setting?" And then you can reasonably expect the GM to either shoot holes in your character details or rearrange his entire campaign to fit your
character you worked very hard on
. Or serendipitously, it's an actual perfect fit.
But back to your question. Tell us about what your character can do (mechanics and stuff), a little bit about the setting, and what you've already got figured out.
Or, you can take another approach