A thought: The fantasy world has a culture where eloquence, in speechmaking and other conversation, is desperately important, and seen as a core skill for leaders. And the King has none of that skill. He can memorize, but he can't create. So your character is the King's speechwriter--a deep, dark secret He lives on one of the king's estates, posing as the gatekeeper for the most distant gate or something of that sort, living in the little gatekeeper's house in the forested end. And his every need is provided by the king, in exchange for the speeches that he sends back. This requires a little tweaking, because he'd need some innocent reason for regular deliveries to the King.
In a feudal society its unlikely he'd own land, unless he was a knight or other noble , but he could be a farmer with slaves or minor servants to do the majority of the work on the land he tenants from his lord. the issue with that is that mostly the farm houses of an estate were clustered in villages as a defense against attack , and to share resources - the spread out farmsteads we see today came later. So if hes dwelling in solitude it makes more sense for him to be a hermit monk living on alms or similar (also most farmers wouldn't necessarily have been that literate - the estate would have had a clerk who did the written records)
It's only mandatory that he lives isolated, because he has hidden rooms below his house where he imprisons and tortures his actual victims. Living isolated is also a good way to not be seen carrying them in, and carrying them out to dispose of the bodies or remains in places where he can be sure they'll be found.
Oh, so you're like a kid I had in class the other day who thought the Middle Ages happened in the 1950s?
Evil lords in the Middle Ages generally had castles for that. And since every lord was law on his own manor, as long as the king didn't hear/doesn't believe tales of screaming injustices, a man like your MC could generally get away with all sorts of highhandedness. Heck, Edward II himself was imprisoned and murdered in Berkeley Castle--- unless you believe the alternate history that he was forced to secretly abdicate and smuggled off to and died in Italy. Moreover, the wealth of the nobility in the Middle Ages was based on land, not money. For a man to be rich he'd own property, and lots of it. He'd have at least one castle/fortress/manor house, complete with retainers, servants, and serfs to farm his land and keep the income flowing in. As @jannert has indicated, he wouldn't make money by selling his books, because the system of printing and distribution and general literacy hadn't developed yet. So you have to consider that if a man like your MC (wealthy, noble, well-known for his cultural accomplishments) were to live as you describe, he'd be very conspicuous and raise immediate questions, even without his little side activities. And you'd have the sustenance issues on top of that.
Actually, no. The codex became current well before the fall of the Roman Empire. I know of no Medieval scrolls, not of European origin post-1000 AD, at least, and if you've heard of any, link to them and add to my knowledge. The codex form was popularized by early Christians who found it more convenient and portable. Citing http://www.historyofinformation.com/narrative/roll-to-codex.php Bookbinding assuredly did exist, all done by hand. If you don't think there were bound books in the Middle Ages, I invite you to check out the Book of Kells at Trinity College, Dublin, or the Lindesfarne Gospels at the British Library in London, or any number of pre-Gutenberg codices in the Bodleian Library in Oxford. Well, no, they won't actually let you check them out, but you can certainly see them with your own eyes.
The reason I suggest the 1700s is because that is a time when the aristocracy still had a lot of power (again, the lord of the manor was still the magistrate for his territory under his holding), communications were still dependent on the speed of a horse or a sailing ship, there was no police force, the surrounding peasantry would still be superstitious and/or minimally literate--- in a way, things were still very much as they had been for centuries before. On the other hand, the novel was starting to be popular as a literary form, and the Gothic or horror novel especially so. The romanticisation of Nature had begun (you see this in Marie Antoinette's creation of an ersatz rustic village at Versailles, Rousseau's idea of The Noble Savage, and Capability Brown's landscaping). The Enlightenment had begun, and it was almost expected for the aristocracy to dabble in scientific or academic pursuits. So for a wealthy landowner of the latter 1700s (or a fantasy period like it) to retire to a woodland cottage on his own estate to produce his writings would be understandable. He'd just be one more scholarly lord with a taste for the picturesque.
I've been considering for a while ramping up the time period even further than that, into the 1800's if I can still make sense of it. This is because this story being in the middle ages actually makes me deviate from one of my original goals: to create a world where most of my stories take place. Several of the ones I've already written (though not quite finished) are set in that time period. One of them even involves trains (locomotives) as a novelty piece of technology (so, late 1800's if I recall). Now, if I was mostly ignorant to how monarchies worked through the middle ages, I'm completely blind to how they worked in the 19th century... Probably hard to cause a civil war too. I don't mind ditching that if I have to.
By the 19th century in a lot of countries monarchs were becoming much less relevant in how the country is run - Britain was essentially being run by its government much as it is now , except there was no real representation for the common man , the principal parties were the tories (not the same as the modern day conservative party) and the whigs (fore runners of todays liberals) - France was in the grip of first revolution(where royalty were executed) and then empire building by bonaparte and so on. You could certainly still cause civil unrest and possibly war by assassinating a king or major statesmen - after all WW1 at the beginning of the 20th century was sparked by the assassination of the arch duke of austrohungary , but formenting a civil war would be harder as most states had state armies by this point. ( I supose France could have spun into civil war had the English attempt to invade from the south near tolouse to restore the royalty been more successful)
