I wrote this like five times and it had several paragraphs and examples and shit. But uh, good rule of thumb is to keep it simple. So I will.
Simple as pie.

In every story, there's characters. And roles. Roles that need to be filled.

How do you fill a role?
As simple as I can say it, it's probably better to not try when filling roles at all. I mean, someone needs to be a protagonist and sometimes someone needs to be an antagonist, but most of the time, that's just something you know when you start designing the story. You'll have to make characters to fill certain roles obviously, but I've always found that it's pretty damn easy. Just make a character without thinking too heavily about the role and then shove them in it. I say this because most of the time when you tailor someone to a role heavily, you usually end up shooting yourself in the foot and someone will scream, "CLICHE." or "STEREOTYPE." or "THAT'S PRETTY GAY, BUD."
So basically when I say, "I need a role." I go off and start designing something that looks cool or awesome or has some sort of dynamic I can work with to do something awesome and provocative. Then I figure out how to shove them in the role I need them in. Like a bartender or something. Then I see what I can do with that to make that character stand out. At least for a bit anyways.

But that's not what I came here for. I need input. How do you fill roles and design characters for these roles? I'm sure of all of my infinite wisdom that I'm doing something wrong.
Oh uh, and pay attention everyone else. I'm sure someone will say something that can help you make your game juicy.

That's a good question. I usually make characters first and try to make them fit in somehow, if I can't I throw them away.

I tend to take the classic stereotype needed and add a personality quirk or two. (Healer. Also collects stamps. And is afraid of cats.) Voila! Role filled!

Of course if the role is going to be more fleshed out you'll need a few more quirks but for a quickie that tends to be enough. Have the stereotype and add something small that makes him/her stand out a bit.

Ah but the Mad Baker had his mind set on another type of role... a tasty PAYROLL!

I often start with an idea of some cool mechanic and then build the world around it. Like if I wanted 3 different classes I'd need 2 genders. Those 6 people would need personalities based on their chosen path, then they'd need someplace in the world to hail from. Why does this place exist? Why are they here now? What purpose could they serve? And how will they deal with it? The game just snowballs out from there.

- Mike

i've never thought that roles was a great way of looking at a story. that's always struck me as a way to fall into the typical writing traps. it makes you feel obligated to create certain types of characters rather than simply create characters that you find interesting. i'm not saying that you're going to make bad characters by having ROLE characters. i've written some pretty interesting characters this way, but i'm a lot less likely to do so. it's a much better idea to create characters from the inside out, rather than the outside in. the inside of the characters is where the depth lies, and will typically make for stronger characterizations if that's where you start. it can be a bit problematic trying to implement proper character depth if you begin developing the character using mostly superficial, unspecific terms and thoughts.

on some general level you need a certain degree of protagonists and antagonists, but i always think more along the lines of how interesting i think it would be to have certain types of human attitudes in the story i'm aiming to tell. the essential relationships in my stories are not derived from how i perceive the "roles" that need to be filled, but by the vastly different ways people could perceive the things that are happening in the story.

I often look to books when I consider making a character for a role in my games. I read a few books that follow the same sort of theme and then look at how the books uses them as a tool to create opportunities and changes in the main character. Then I try to apply that with a character I make in the game and voila... my role filler.