Creating good characters

With Halloween ending, we say goodbye to all those monsters we dress up as every year. So long zombies, witches, and vampires! But what makes these characters so memorable? What makes us tell the same scary stories over and over every year? How does one bring your characters to life like these beloved monsters? In every good story or script you need characters. Sure there's the protagonists and the antagonists. But what makes a character relate able and not just words on a paper.
A good protagonist is usually more righteous than normal society and the antagonist worse than normal society. A character has to be someone your audience can identify and see themselves in. You must give him a back story. Who is he? What does he stand for? who does he fight for? Does he have loved ones, like a family? All this should help you build a character.
You also have to make sure that everything you are adding to the character makes sense for his story. We have all seen movies when the story has an unnatural turn and immediately takes you out of it. Always make sure your character is doing what comes naturally to him/her. Once you have well structured characters, the plot of your story pretty much writes its self.