Well, again, I don't write fiction.
I did for a while blog in the voice of a dog. I think I was pretty convincing, actually, under the circumstances.
The character must be seen. Their personality must be consistent. They must act in character. Some characters are like the people we have met. They might look like them. Good and bad characters are all around us to use as we write. Who have I disliked, and why. Who have I loved, and why.
I think it is a connection with the reader either as a protagonist, antagonist or passive character. One has to know their audience as well. If an uneducated ditch digger in India is your audience; writers or orators cannot be using high brow vernacular... and the same is true if it is a high brow or specialized audience. One cannot write as a undereducated dolt and expect to reach and keep the audience's attention.
Always from real people, friends and family, they know I do it and they love it.
Those people bumping around inside my head have to feel, become disgusting and heroic through their flaws and terrorize my psyche until, unable to sleep or be completely awake, I give up ground and write them down. It is little enough to make anyman scream.
Real life emotion and being human.
Characters must be people the reader can relate to on some level. They must be someone the reader can get into and care about so that they can suspend disbelief. The villain (assuming there is one and there almost always is to some degree or another) must be the same. Even the reader absolutely hates them they should still be someone the reader can relate to and understand even if it's on a primal level. Each should have 'good' and 'bad' points. No one is perfect and your main character shouldn't be either or no one will believe in them.
Don't take my advice here. I'm one of the very lucky ones in that I don't create my characters. They create themselves. They come to me with the story through CC, each with their own voice and mannerisms. Each with their own stories to tell which make up the whole. I am merely the tool they use to do that.
I haven't written fiction books where the characters are most important. However, I have included a few brief, narrative scenarios in my book to more or less illustrate the nonfiction subject of the chapter. The two or three characters I created were realistic in how they talked based on their location of residence and their activities. In my opinion, for a character to be believable to the reader, what a character is involved with in a story must be believable; in other words, it could happen (or has happened) in real life. The character must instill a sense of reality to the reader. Unless it's a science fiction story, the character must be similar in human nature to real people, and what he or she does must relate to what a real person might do, whether in the same or similar circumstances.
A believable character is one who you can identify with. Someone who has normal attributes and a common lifestyle, but is put into a situation that is special enough to write about, or to read about.
I create characters for the situation sometimes, and othertimes I create a character based on someone in my past, or that I have known, and sometimes I just pull him/her out of the ether. Depends on my mood, the storyline, the genre, etc.
A sense of the character's vanity and weaknesses helps his or her credibility.
I tend to torture them a bit, then see how they react.
to make a character believeable, you have to add flaws, and lots of them. i create my characters way before i start writing the story, i describe how i want them to look, act and feel...THEN i begin to write.
Since I mostly write nonfiction, I can't be said to create my characters. Wherever possible, I use their own words and actions to make them believable.
For a character to be believable he or she needs to be relatable. Even an unlikable character needs to give the reader some way to empathise.
A character has to be multi-layered, with contradictions and flaws; with a full backstory and enough involvement in whatever scene or set of scenes in order to act as a force or counterforce. Equally important, a main character at least should have a subtext, elements beneath the surface that even she or he isn't aware of and only come into play under pressure. In my work, characters seem to evolve and, strangely enough, want to come into the story, even insist on playing a part or showing some other side to their nature I never knew existed. When they prove to have a life of their own, when they enter and truly "exist," they've earned the right to be seen and heard.
I start usually (not always) with someone I know at least a little, then diverge and add. To make a character believable, he or she must not be one dimensional. Quirks, flaws, a back story, individualized dialog all help, along with good physical description (not necessarily direct telling of height, weight, eye color, etc.)