I create a character that I need for the plot. One always hopes the end result is a believable character.
Personality is needed that is different from every other character in one way who also has flaws. I create my characters by taking bits and peices of my friends that I love and hate.
They have to be real. In other words, they need to have all the bumps and warts that we all have in our personalities. I creat mine by becoming the character. I put myself into the situation and ask what would I do or say at this time. It works for me. The comment I get most often is that reading my books is like hearing from an old friend and catching up on what is going on in their lives.
I don't really create my characters,they create me. They take control of my mind, my soul and my life until they have life and soul of thier own.
That's a tough question, but I would have to say resonance. We have to feel like we could know this character to care what they do or what becomes of them.
The girls, the boys, the animals, the heroes, the murderers, the suicides, the lowest and most pathetic loser--every one of them is me, or elements of me parsed out and exploded. That said, I modify these with aspects of interesting people I meet while traveling, and my imagination, for dramatic effect.
You see why I maintain that all writing is therapy?!
I believe you need to make your characters as real as possible by giving them similar traits you feel your readers will have in their own lives.
You must give them a sole to live within the pages of the story.
Reality is a must. Create an honest non fantasy experience that determines how things appear to you rather than as you might want them to be.
I admire those who write fiction. Writing only non-fiction relieves me of the need to make my characters believable.
My characters are revealed to me. If they are believable or not does not concern me. They are created for me and the reader.
This is simple, really it is: the person needs to be real. Every character I have is based on a real life person. Every nuance, every shake, shutter, blink of an eye. Every detail is based on a person I know in real life. If a writer wants their character to be realistic they have to be real, as soon as they step away from the reality that they see to imagine a character, to conjure them, then the character loses that authenticity. This doesn't mean that a character that is supposed to be a superhero can't be a superhero, but the personality, the image of that person, that character, should be real. That's why I like Batman/Bruce Wayne. Bruce is a realistic character. He acts snide and snooty the rich boy stereotype. As Bruce Wayne he is the face of the rich and glamourous, the same face we can see on the news in real life out of Hollywood. The alternate ego, on the other hand, (or maybe the real person if we consider that Bruce Wayne is the alternate ego), Batman is also realistic, because where Bruce fails to show his anguish and anger and sorrowfilled desire for his parents, Batman can. Batman is capable of acting on the whims of that anger and anguish and the need for vengeance.
Realistic characters don't need to be deeep, they don't need to be the overly dramatized ideas of what most people think a character should be. When you base a character off of real life people, the deepness will come out without ever needing to force it.
The character must actually exist. I make nothing up.
I find inspiration for some of my characters from people I have known. The main character in "The Cielo" was inspired by my cousin. She told the story of how she and her family were trapped in a farmhouse in the hills of Tuscany during WWII, but it was more than that story that inspired me. It was my cousin herself, a feisty little woman who I am sure could have fought off some Germans singlehandedly.
They must be believably real. Mostly from life experience.
For a character to be believable, you have to write them honestly. You have to know all about them, their background, their beliefs, their foibles, their habits - they all come to bear in the way they present themselves.
Do they pull their ear when they're thinking hard? flip their hair? Do they hate their name? Despise spinach? All things that make them more "real" for the reader.