Unlike some, perhaps most, people think, a character is not simply a name, age, and description. A character, be it for a story, rpg, or whatever, is a working progress. A character is never complete until the story ends, and even then there is always room for more development. The creation of a character can be hard for some, easy for others, the funnest part or the least fun. It all depends on who is creating the character. Whether it is easy or hard, fun or not, the initial creation is a crucial part, for in it you are setting the foundation for the rest of the story that you are sending the character through. Of course your character can change over the course of the story. It's really if your character doesn't change that you should be concerned. Your character should change, because if he doesn't change, what was the point of the story in the first place? A good character will always be different in some respect at the end of the line, for better or worse is up to you.
One of the biggest temptations you might have when creating a character will probably be to make him perfect. I can tell you right here and now, don't do it. A perfect character is not only boring, but also unbelievable. Nobody is perfect. That is a fact, no arguing it. Therefore a character who is perfect loses just that much believability. And as for boring, if you're perfect, what is there left to achieve? You may say, "Oh, well, my guy doesn't have this, that, or the other thing" but that's just an excuse. That might be what the character wants, but not what he needs. Take a look at some of your favorite books. Do they start with the main character longing for something, or maybe being appointed a task they have to accomplish? Probably, that is how most books start. Do they end with the character getting that thing, or accomplishing that task? Again, probably. Most books have happy endings. BUT, and that's a big but, does the character come through the story unchanged? Did the character go through the story perfect, or even flawed, and end the story still perfect, or with the same flaw, the only change being that they have that missing thing? Probably not. Because if the character doesn't achieve anything worthwhile (I do not put any thing under worthwhile), what was the point? Again it's the point of change. The character must change. And if the character starts perfectly, there's nothing to change, and therefore no point.
After creation it isn't all fun and games either (although it is for the most part). You have to stay in character. You can't have your quiet and shy character run up to a complete stranger and start laughing and joking with said person. Or your brash and rash character cautiously approaching a situation. Either case works in direct contradiction with how you had your character set up, therefore destroying the any reality that you might have had. Not only that, it makes your reader or fellow players (if it’s an rpg) lose all confidence in that character. They can no longer be sure how the character would react in any situation. He might fly off the handle when your reader expects him to respond quietly and rationally. He could very well blow the bad guy to pieces rather than offering the expected mercy. You must avoid that at all costs. You can have your character do something directly against the personality that you have built, but only, only if you have built up to that point throughout the story. Otherwise your credibility with your reader and/or fellow players is out the window.
But creating and developing a character shouldn’t be work. If it is, you should take another look at what you’re doing and ask yourself if you really want to be doing it. Creating a character should be a fun, challenging and maybe revealing experience. It’s a chance to be someone or something that you can’t be in real life. A chance to let your personality quirks to shine bright. Or if you don’t want to be anything like yourself, you can try out an opposite of yourself, just to see what it feels like. In the process, you just might learn more about yourself then you thought possible.