Suppose A is a famous historical character with a known history of emotional attachment with a particular set of people. If I would want to write a fictional story about character A that might involve distortion of the actual incidents of her/his life, will it be okay?
How much is too much while handling a fiction plot based on a real historical character and what points should I care about?
Is it okay? Well, it's likely legal (if the person is long dead anyway, and probably even if they're alive). You can do it. You might even get it published.
For a large number of readers, the answer is that, no, it's not okay. Though what percentage of that really depends on the details. Fictionalization of historic events is extremely common and things get really bungled.
Take the excellent book Hidden Figures, about black women employed by NASA as mathematicians and engineers as the first space flights were planned then executed. The author interviewed the actual women involved (those still alive) and many others who lived through that time period.
The book is nonfiction and, as far as I know, pretty accurate. Then it was made into a movie. The movie is wonderful and worth watching but, for those of us who read the book, it involves a lot of handwaving. They took characters that worked in different decades and made them all similarly aged friends in the same year. They completely changed character arcs to aid in the drama. For example, one movie character fought for years to become a supervisor (the white woman in charge refused to allow her) then finally got her promotion in the late 60's at the end of the movie. The real person with that character's name had been a supervisor starting in the 40's.
This sort of distortion is extremely common in movies, whether based on books or on historical research. Sometimes involving huge changes like putting together events that actually were a couple hundred years apart. It's not as common in books, but it happens.
So is it "okay" for you to do this? Well, yes and no. The question is, what can you get away with and who are you pissing off? If you add in scandal or things that might be libelous were the people still alive, you could be in trouble, even if legally you're in the clear. I mean, don't write a novel about Princess Di's early life as a pole dancer.
But a work about William Shakespeare in a relationship (that never really happened) with a woman who disguises herself as a man so she can take female roles in his plays only ever played by men (also never happened). YAWN Been there, done that.
I am one of those readers that hates inaccuracies like that but I still loved those two movies. I'm stricter about the books but often read and enjoy them anyway. It depends how—and why—it's done.
Make your choices meaningful. Don't change things because you're too lazy to research. Change them because they work better that way for your story.
Getting your facts straight is one of the rules of literature. As with the other rules of literature, it is one thing to know the rule and know when to break it, but another thing to ignore the rule when it's needed. In the case of this rule, there is no substitute for knowing what the facts actually are. Only then can you justify presenting a different version of reality in order to serve the story. This is different from acting as if the facts are either not important, or as if you have rejected the facts because it does not suit you to accept them.
If you want your story to have an element that contradicts the best-supported version of events in the historical record, you should make it very clear (in some way) that you know what the record really says, and that you made this choice in order to explore a story with different conflicts in play.
If the historical record is well-known, and there aren't already an army of cranks who are pushing an alternate version of things, it may not be necessary to explicitly state that you are presenting an alternate history; everyone will grasp it readily enough. For instance, if Confederate States of America wins the American Civil War in your novel, everyone will know you are writing an alternate history and don't have a fringe agenda.
On the other hand, if the topic is already the target of politically-driven revisionism, you definitely should make it clear that the version of events in the tale should be seen as fiction. For instance, if you want to write a novel in which the Holocaust did not happen, do not fail to stress to the reader that you believe the Holocaust abso-{filtered}-lutely did happen.
In another case, it may be that the facts as known to history are familiar only to historians. So if your story has Julius Caesar married to a woman named Desdemona, someone unfamiliar with Roman history may "learn" this to be the case, and you should take the time to prevent misunderstandings.
Another case that requires a warning is when historians are honestly divided on what actually happened, non-historians are pretty much ignorant of this fact, and your story presents one of the versions vying for acceptance. In that case you would also want to advise the reader that the version of events you present is not the only reasonable interpretation of the historical record.
As to where you put this caveat lector, a brief author's note at the beginning should suffice.
Shakespeare did it. Richard III was not a homicidal maniac killing young princes. He was an able king.
The movie Fatherland presents an alternate history where WWII never happened, Hitler is an able leader and JFK is an aging US President. It all works well because it had a purpose. History did not quite suit the needs of the story, so history changed.
If A is the focus and you change him/her from respected figure in history to raving lunatic, you might have a problem. Depending on how far back in history your figure is, there could be descendants who feel the need to defend the family honor from defamation.
If you change that A never met B and C, that is not a problem. Historical fiction is fiction with sometimes just the gloss of history on it.
Do enough research on A that he/she is recognizable as A. If I were writing about Napoleon and depicted him as a slacker with zero ambition and very little intelligence, I might as well create a new character since we know he was driven, intelligent and ambitious.
If you want to create a scenario where A is clearly A but different, ask yourself what traits are essential to A being A. If you take my example of a stupid Napoleon, intelligence must be returned to him to keep from breaking reader immersion. Napoleon might remain a talented general but never take the throne, never become Emperor.
What makes A who he is? What changes do you wish to make? Might said changes be served by creating an observer character who comments on events?
What are the limits? You set those, but if he has living descendants, be careful of defamation as heirs have been known to defend the reputation of the dead.
History is a fluid thing. Even now, historians have different opinions about what exactly happened, and what motivations people had for their actions. So there is basically no way to write a historical novel that won't be considered inaccurate by someone.
But your question is "how much is too much". There is no clear answer to this.
Some stories take a historical character and completely change his story. "Abraham Lincoln: Vampire Hunter" is one example. These stories tend to add obvious fictional elements, like adventures, fantasy creatures or other things that clearly aren't considered real history.
Other stories fall into the "alternate history" genre, where you deliberately change something in order to explore a story in this changed world. In this genre, you would generally point out the things you've changed: The plot summary might read "in a world where the Opium wars never happened, a young emperor tries to...". In this type of novel, your reader will assume that everything that was needed for the change, and everything caused by the change, is fiction.
If your novel is generally a realistic story about your character and his time, I feel like you have some responsibility towards your reader. Many people form their image of historical places and events by reading novels, so they will absorb whatever you write. Think of all the people who watched the great movie "Amadeus" and now believe that Salieri was Mozart's deadly enemy. He wasn't!
A little bit of distortion, like making some events happen closer together, or leaving out some minor characters, is necessary for most stories. But if you are going to change major things that would make the character appear very differently from what we know about him, it might be good to add an explanation of this difference in a postscript. This will also let your more historically informed readers know that your changes are deliberate.
As other answers have noted, if the character is relatively recent or is a revered figure somewhere, you might get some backlash about portraying him "wrong". In some cases, this might become a real problem for you. That's always worth considering.
But generally, just write the story you want, and if you make big changes, just point them out.
There is a whole genre of fiction which explore what would have happened if certain historic events turned out differently: Alternative History. If you market your work as part of this genre, then anything goes.
But this genre usually focuses on changes which have lasting consequences on a global scale, not just the lives of a few individual people.
If you claim or just imply that your work is historically accurate, then anything that contradicts historic consensus will be perceived as a research mistake on your behalf and will likely be seen as a flaw in your work.
The main question is whether your readers will accept it and that depends on two factors:
a) how well is the actual history known
and
b) do your represent your work as historically accurate or as fiction based on history ?
If you make it clear to the reader that you are taking historic events or persons and waving a tale of fiction around them, diverging from actual history, then the reader will not feel cheated.
The world of fiction is full of such stories, and many of them are well received. Stories that claim historical accuracy but don't deliver it are either well received because audiences don't know better, or critized if they do. Often both because a small fraction of the audience knows and complains, but most don't care.
So if your historic person/event is well-known, you should make it clear that your fiction is not the real history. If your person/event is obscure, you may get away without such a disclaimer, leading the reader to believe you are representing historic facts. I personally would advise against it, but it's not like it hasn't been done.
