Usually some trait or quality people can relate to, like a scar, or a bad habit.
I create mine from some of my own experiences, for I feel that in order for the reader to grasp what he/she is reading, it has to be convincing.
To me it is dialog that creates believability. My characters have to speak in grunts and short bursts, and they have to curse a lot.
I think that the believability of a character would depend greatly on the type of story, or the particular genre that the story belongs to. As for fictional westerns, people have always looked for the good guys and the bad guys in westerns. I think that mixing a little of both characters together makes them seem more real, there are very few folks around who are all good, or all bad for that matter.
The characters that I create for my stories come from those pictures in my mind that come purely from my imagination. For the most part they are created in my mind however, occasionally a character that I am writing about does bring to my mind someone that I know, or have known I guess that’s because I rely on the attitudes and demeanors of real people when I create a new character.
The only requirement a character needs to be believable is for the reader to have an open mind. You can create any kind of character you want but if the reader doesn't want to listen to you, then you've failed. And so describes the talent of a good writer, making the reader want to listen to him.
Characters create themselves. Just give them a name and let'um talk. If they're real, they'll walk and talk their heads off. Jim Buller in THE BEAR CAVE is an Agent with the FBI who clings to the routine. His novice partner, Sharon Forrest must elbow her way around "the Bull" to rise above that routine. The interaction between them is the friction that moves their tails (tale) as they face the bear in the cave.
I give them a personality without describing it. I have them eat chocolate cake as though they are making love to it, for example, so you can feell that this character does everything with passion and enjoyment. I describe their physical reaction without telling you that that character is one way or the other. I like to hear how people see my characters. Friends have given me so many different points of view and usually feel some type of affinity with my characters. I like that.
The requirements for a believable character are currentness, details, and reactions. Currentness being that the character talk and act like his/her time period's average person. If it's a teenager in 2005, then he/she should talk as such and act as such. That brings in details. Things like where the character would go to eat, what their favorite color is, what their habits are. These things don't have to be blatantly said, but the reader should know them anyway and ask themselves, 'How exactly do I know all these things?' Last, the reactions are necessary. Your character cannot react like any other person because then the character becomes boring and already known. You want this to be an entirely new person that the reader must figure out in order to understand. Nothing should be predictable.
I create my characters by analyzing myself and people around me first. I create someone that they are so tediously defined that they don't have a single interchangeable factor about them. These characters need to be bright, shining new faces to anyone that reads about them.
I'm a nonfiction writer, so there's no question my subjects are believable (geesh, I hope). Some of my books are for the educational market, so reliable sources are paramount to the book.
The easy answer is realism. Think of someone you've known, preferably an outstanding individual, and using your five senses, create him mentally down to the crooked little finger and bunions. Don't write a long description in your story, it's only necessary for you to know him.
Memorable characters which become interesting have problems or "blemishes" of any type.
I create them as I believe they should be.
I think it works best when we use a character that is based on someone we know. That way we won't have the character act in a way that that person would never act. We need to understand about personalities so our characters won't appear fake. I create my characters from my life. That way I know the character is believable. Someone once told me that something one of my characters did would not happen in real life. I said, "Yes, it would; it did."
First off the author has to believe the character so, I start by giving a first, middle and last name, even if I don't use them in the story. Then I think what kind of person they are and how they will change or develope in the story. I decide if I want a hero, heroine, villain, or victim. With the aspects of the story such as what they might say and how it should be spoken and how these things will develop within the story.
The reader must be able to slip the character's mantle comfortably over their shoulders and move freely. I create my characters the same way, and then challenge them with the circumstance of the story in which they are enmeshed.
I have read and been told the way to make a character work is to believe in them. What I do in my works is see the world through their eyes as much as possible and from there the story is born.
I often base them on me. Or at least on others I know.