I'm going to do a short series on my own rules for writing historical fiction. Now these are my rules. I obviously can't and won't try to force them on anyone else. In at least one case, I wish I could.
The one that absolutely infuriates me when it is violated is the first one. If you want to get me to despise you (and yes, I mean you, Mel Gibson), violate this one:
If your historical fiction is based on real people, be responsible to the originals and the people who care about them. There are usually gaps in the historical record, often large gaps. Fill those in. Make up reasons why they did things. Make up emotions which they may have had. Make up conversations and encounters they may have had.
All those are fair game. You can even fudge a bit by saying Washington got to the capitol two days before he did for his inauguration. I'll say, it's fiction; you're within bounds. But do not change major events or accuse them of despicable acts they did not commit.
Do not say that Robert Bruce was a coward who only fought the Battle of Bannockburn because he was fiddling around with a piece of cloth. He had for f****** sake had THREE brothers hanged, drawn and quartered by the English, had fought the English for eight years and had planned for that battle. Don't say that the Bruces betrayed Wallace any more than you would say that Washington was a traitor who conspired with the British. And saying that William Wallace was the father of a child born seven years after his death makes you look -- stupid.
This is only one example, admittedly one that particularly irritates me because so many people bought the lies in "that movie", but it shows why you should NOT do it. You will make people angry--who aren't going to buy your your next book if you do. Whether it is William Wallace, George Washington, Robert Bruce, Mary Queen of Scots, or Abraham Lincoln, there are people who care when you twist the facts. Be careful in handling real people in your fiction.
There are certain historians who say you shouldn't do it at all. They're delusional in my opinion. Real people, including national heroes, have always been the stuff of storytelling. That's not going to change. And I'm not saying to treat them as perfect. That would be boring and as much of a lie. If they did something people consider wrong, tell that, too. If they could reasonably have done something wrong--something that isn't contradicted by known facts--you can consider making it up, but I still say take care. (And I mean reasonably, not a seven year pregnancy!)
I am just saying that don't assume that no one will care if you ravage their reputations. Keep your own conscience clean by not slandering them.
My own novel, Freedom's Sword, is based on the life of a true character, Scotland's Andrew de Moray. I worked hard at writing a good story around the facts of his life. You can find the novel at Amazon, Barnes & Noble and Smashwords.