What does he/she look like? What makes him her important? (If anything)
There are so may question that need to be answered. So times when character appear in a story, they just don't seem real. That is the worse problem ever know to author and it needs to be fixed. RIGHT AWAY!!! If you have an unrealistic character drop everything and run to fix that as soon as possible. One bad character can ruin a whole story. When you have a poorly developed character, it will not be ok this once or no big deal. Not matter how minor the character is, he or she needs to get fixed or else your story will suffer. ALL THE STORY!!! One mistake can ruin a story which is why you need mass edit before you ever even think of publishing. Poor characters will leave your reader with a bitter after taste and no matter how epic your story is, the character must be good two. You must work very, very hard on your characters because it's easy to tell how much time you spend on a character by how realistic it is.
Your Villain can't be pure evil. Yes, he must he must be evil, but not purely and horribly evil.
Your Hero can't be the perfect example and neither can your mentor. You Hero should not be the best ______ in all the land! That is a huge no! You're hero must be a normal person how was thrown into a plot because of your villain. Maybe you're writing romance and the villain hurts the love in some way so that the hero feels the need to stop the villain and make the love have a better opinion of the hero.
Maybe your writing fiction and the villain does ____ and the hero has to stop it.
Almost any story is about someone bring something to an end.
Make yourself a list of question that help you think about characters. As a writer, questions are your friend they bring your story to life and help you think about your story. ALWAYS remember questions.
Here are a few examples:
What is his/her background?
What is this person hiding? Why?
Does this person have any connection to the villain?
What impact does this person have on the story?
What is the purpose of his/her appearance in the novel?
Will this person (privately or publicly) help fulfill the story goal?
Does this person help the villain in any way? If so, Why?
What does he/she have to lose? Are these things important? How important? What is he/she willing to do to keep it?
Did he/she know who the hero was before they met? If so, who told him/her?