Honesty. Realness. Believability. I think the most difficult genre to write in must be science fiction. Not because of the lack of imagination, but in translating that imagination into reality, into a believable interaction with the reader.
A weakness. If they have no weaknesses, they you can't relate to them. They also need a set of moral code they follow. Obviously if they are the villian, their moral code won't be what the hero's would be, but they need some sort of morals or guidelines for life that they follow.
The morals my characters have takes shape as the story does. When situations arise, I have to ask myself, 'how would you expect this person to handle this situation in relation to their personality and morals?'. It is an evolving process throughout the entire story, but the foundation is started in the beginning. Plus part of the pleasure of writing is to 'meet' the characters as they evolve...I get to know them as I write, there personality and morals aren't set in stone from the beginning.
I map my character out very well. From the hair color, their occupation, the pants they wear to the things they say (i.e. are they going to be a classy character or very urban- like).
An ability to understand and forgive humanity is essential in any author. Some of the best authors write themselves over and over again, and at once condemn and forgive themselves. Some of our most revered and favorite authors - Kurt Vonnegut, Henry David Thoreau, Ernest Hemmingway, J.D. Salinger...
I think there's inevitably going to be ego and self-referential characters in any work of fiction, no matter how hard you try to avoid it. Whether your avatar is the hero or a cameo, it doesn't matter. I think you have to have something genuine, genuine growth, genuine pain, something real. It can be muted by fiction, by different characters or context, but there's something real that has to be sewn into the story. That's what makes writing an art, and that's what makes characters believable.
A believable character is a character that readers can relate to in some way. I take aspects of my friends and put them in my characters; it gives them more depth. Human like and not fictional.
Real weaknesses and real opinions.
Well I try and think about how the person would really act. If it is a romance I will losely base the character on myself a little. At least reactions that I would have and so on. A good character is someone who others can imagine reacting the way they would in a situation.
My characters are based on real people often - or are an amalgam of people I know. They have flaws, they strive for better, they are capable of change. I think an understanding of the human condition and social/psychological issues is helpful. Being a keen observer of life is essential.
I write non-fiction so the characters are all based on real people and real things that happened. I need to write about what I know so that's why I stick to non-fiction. I can summon up so many memories and specific details and so the stories write themselves.
The reader needs to become a part of what is being read. He needs to be the main caracter in the story, he needs to feel as if he is reading as if it is he that the writer is talking about. Style and questions.
A character must be somewhat human. I write only fiction, so of course I add some powers here and there. I create mine, well based off me and my friends.
whomever is true to life. Don't believe this question applies to this type of writing.
Believable characters require good intentions and flaws, embedded internal conflict.
Making them believable can be tricky at times. For me I will end up with a big list of details, it almost looks like I have created a new personal friend. I know everything about them, likes, dislikes, habits, and every scar or scratch they have. The more I believe my character is real, then so will my readers--I hope.