Lately I've been forced to think about just how much of me is in my characters -- and there is a lot.
There's a school of thought that claims you can deduce what a writer is like by his or her characters. That is, the writer always creates redheads, so you deduce that the writer is a redhead or has always wanted to be a redhead or was frightened by a redhead as a child. Or the characters frequently espouse a particular philosophical viewpoint, which is taken to be the author's. (I think Ayn Rand says that Art Is Meant To Do This, to be didactic. I disagree.) Objectivism aside, I think that the assertion is true only in the weakest sense: you can deduce that the author creates characters like these.
I think there are a number of reasons why we want to believe this. First, if we're moved by a particular piece of fiction or influenced by it, we feel a connection to the creator. We don't want to believe that this character with whom we've journeyed was created from the whole cloth, that these ideals we've come to hold are just dust in the speaker's mouth. The writer must believe, we feel, or we would not have believed.
Second, a lot of writers go over the same ground again and again. If the pattern is repeated, we think, it must be significant.
I know that I go through phases. This being erotica, my phases tend to be on topics more like adultery and sexual positions rather than legal and philosophical grounds, but they are phases nonetheless. I have no great desire to cheat on my wife. I have written (under another name) several pieces about serial killers, and I have read fairly widely about them, but I have no desire to be a serial killer, either.
The datum that a writer's mental machinery finds one set of ideas easier to grip and to work doesn't mean much more than the datum that a wrench handles nuts and bolts better than it handles screws or nails.
So what can the writer's characters tell us about him or her? Much less, I'm afraid.
The mere fact that the story got written tells you that something about the story is interesting enough to warrant finishing the story. "Enough" is the weasel-word here; what it means depends entirely upon the writer & the story. For me, for one story (not present on these pages), "enough" meant the chance to spend hours with a woman I adored. I doubt you could deduce that from the story.
The absence of a particular type of character means either that the writer is uncomfortable writing about that kind of character -- or that the writer hasn't gotten around to a story with that kind of character yet.
Oddly enough, the one thing you can tell with reasonable accuracy (three-fourths perhaps) is ignorance. If the writer gets basic facts wrong, you can deduce that he or she doesn't know much about the topic or that he or she hates research. This isn't foolproof; the writer may know more exceptions than you do. For instance, I had a query about Unwrap Party asking why Sarah's hair was blonde but her pubic hair was auburn. In that case alone, it's because I had a particular woman's body in mind, and in fact those were the colors. (The fact that it aroused question means that I should have sacrificed accuracy for the story, but we all make mistakes as we learn.)
There are also stories where accuracy would just get in the way. For some years, I've had in mind a modern-day sequel to The Prisoner of Zenda: The main character is a thief, just out after his second prison term. He doesn't want to steal any more, it's just not fun. But he's convinced to do one more job to get the money for his retirement, and everything goes wrong. On the run from the cops, he has to buy a fake passport, but the only one that matches his description even roughly is for a guy from Ruritania. He takes it, and the first time he tries to use it, gets deported. Once in Ruritania, everyone has their own reasons for pretending he's really the guy his passport says he is...
This would not be a novel where research was important. This would be a novel where breakneck pace, plot twists, style and atmosphere would be important: a romance in the literary sense, in other words.