It’s understandable in a way. You love a certain period of history, become engrossed in it and want to put yourself into the story. For a lot of readers, it works and they enjoy the results. For me, it doesn’t. Or, at least, hasn’t so far.
I’m not talking about original characters as a whole. There are many books featuring OCs that work extremely well. Hawley Jarman’s We Speak No Treason comes to mind here. The book has its critics, and its flaws, but I have a very large soft spot for it. Hawley Jarman was (along with Margaret Campbell Barnes) my way into the Wars of the Roses and, more particularly, my way to Warwick and the rest of the Nevills. The three OCs in WSNT carry the story, are nameless (two have nicknames) and aren’t disguised avatars of the author. (Or, if they are, the disguise is better than most.)
** [I have a confession to make here. When I was very much younger, my first attempt at WoR fiction was through the agency of a wish fulfilment OC. It was clear from almost the start that this wasn’t going to work. However, I liked the character and the set up so much that I changed it quite dramatically, and now it forms the core of an SF wip that has taken itself in a whole new direction. I feel this qualifies me a little to have an opinion here.] **
As soon as I spot one of the following in a blurb, little red flags are raised:
1. An historical character travels through time. The set up might be brilliant, and the consequences of that journey intriguing, but I know it’s to get the character into the author’s world so that he (usually) can fall in love with her (usually), whatever his marital status might be in his own time.
2. A modern character travels through time. She (usually) can then stun the HC, so that he (usually) is amazed at how feisty (so one of my least favourite words!) she is. She can insert herself into the story as a kind of deus ex machina, and there are no problems about anachronistic real, actual wives or lovers.
3. An OC becomes the secret lover of a well known HC. If he (usually) is known to have had a mistress or two, she (usually) is the One He Loves Best in All the World, despite the fact that her name never comes up in the sources. (Hawley Jarman does do this in WSNT, but puts the relationship between Gloucester and the Maiden on hold during his marriage to Anne Nevill. And while she loves him best in all the world, there’s no suggestion that she is the Love of His Life. And there is a tenuous connection to reality here, the Maiden turns out to be the mother of Richard’s natural daughter, Katherine.)
If the HC is either not known for playing away, or if he is credited with loving his wife, that doesn’t seem to cause too many problems. She is his secret guilty pleasure, the one he can Be Himself with, who can warn him of all sorts of dangers and get him out of trouble, preferably without anyone knowing anything about the part she plays in his rescue.
4. A woman/girl dresses in her dead brother’s clothes to take his place in whatever venture he was about to begin. Often it has something to do with family honour. “Good Lord!” the HC can say. “You’re a woman! And… and… I love you!” That way, she gets to be in the thick of things without all of that tricky reality stuff getting in the way. In her ‘boy’ persona, she can become so valuable to the HC that he would never consider outing her. In her ‘girl’ persona, of course, he can’t do without her.
There’s nothing wrong with lying in your bed at night, or looking out of the train window, dreaming about Being There and Loving Him. The trick is then to find a way to translate that into a form that doesn’t involve any of the sleight of hand mentioned above. Unless it’s the Duke of Exeter that’s your secret fancy, you might try and find a way to identify with the man’s wife, to put yourself in her shoes and write the story from her point of view. (Actually, in Exeter’s case, you probably could make up a mistress if you wanted to. I can’t imagine that he was any more celibate after the break down of his marriage than his wife was!)
I understand the limitations of doing this, writing from the pov of a real wife, and that’s another set of hurdles that can be difficult to get over. (And a whole nother kettle of fish.) But it helps keep the historical in Historical Fiction. Anything else is Alternate History or Fantasy – and there’s nothing wrong with either of these. If an author makes it clear that that’s what they’re writing, then my little red flags stay down. It still might not be a book I want to read, but my reasons will be different.