Characters - vital elements of pretty much any story. Their thoughts, words and actions drive the plot along.
For some writers - and indeed some readers (or viewers, in the context of a movie, play or television show) - a character can seem very real; a character may endear himself/herself to the audience to such a degree that there'll be an outpouring of grief at their demise, just as though they actually existed in real life, and I've heard a few writers say "I no longer have control over what he does - he has a mind of his own". (Indeed some characters may be real-life people - all of them (at least theoretically) real, in the context of non-fiction). For some other writers of fiction the protagonist tends to be the writer projected into a certain situation, plus whatever changes to the physical constitution, personal background, etc the writer considers appropriate.
How does one come up with characters? What is the genesis of the characters in a given narrative? In a conversation on this very topic I had with a friend a while ago, we were more or less of the accord that the protagonist tends to be based on the writer in some way (though naturally there are exceptions to the rule), and indeed all significant characters contain at least a piece of the writer in one way or another. I can honestly say that, at least in the novels I'm working on, at least a couple of the heroes have been modeled on me (albeit with some changes) and in Breaking Point a few of the heroes and anti-heroes contain elements of me. In my other project (tentatively titled "Memphis") the heroine Lucy was modeled on a friend of mine who had the overall look reminiscent of a flapper, but at the same time looking like the girl next door; however, Lucy no doubt contains at least one or two pieces of me, or at least my ideal woman. I'll admit it, my villains tend to embody that which I despise or detest, which is why my chief antagonists are narcissists with a cruel streak, and also tend to be cowardly and treacherous, and know how to turn on the "poor me, nobody understands me" act. I think I can safely assume that it's the case with a lot of writers (but I welcome intelligent, constructive feedback on the subject).
Needless to say, the characters have to be believable, and the more engaging the better. Indeed, to write a character that arouses strong feelings in the audience - a hero or heroine or even anti-hero that inspires love or a villain that inspires loathing - that would be something. Even having the reader understand the protagonist and thus sympathising is a sign you've done something right. As long as there's depth to the key characters, and believability, this is achievable - what world they're living in, where they came from, how would they act or react in this situation (and in comparison to how you or I might behave) and so forth, plus that something which the reader can identify with.
