I love the idea of sages in a fantasy RPG. That scholar in their study with vast piles of paper, strange artifacts lying around, books half-forgotten, manuscripts half-written, quill pens and half-dried inkwells, perhaps the scholar themselves hard to find in all the clutter… The image evokes mysterious, fascinating knowledge, and the pursuit of knowledge for its own sake — two concepts dear to my heart.

The problem is, I can never seem to make that sort of person fit within a medieval milieu. Is it really possible to make a living as a sage? Seems like consulting for the occasional adventuring party who swings past is unlikely to produce a reliable income. Or maybe the sage themself is a retired adventurer with money and lore money squirreled away somewhere? But then, rumors will spread and next thing you know, they’ve been robbed. Or if they’re a powerful mage, then rumors still spread and they wake up surrounded by angry people with pitchforks. So how can this kind of person actually work in a medieval setting? Here are a few ideas:

1. Temple librarian: Many religious centers end up becoming repositories of knowledge; there are real-world examples of this. And there will often be archivists in charge of keeping track of it all. These people will accumulate knowledge almost automatically. They may be under pressure to conform to religious dictates, though, and sometimes end up doing tricky theological gymnastics to excuse the preservation of heterodox texts.
2. Court vizier: An educated ruler, or one who just understands the value of knowledge, may deliberately curate knowledge. And they may find a specialist to keep their collection of that knowledge. Such a person will have protection from anti-intellectuals, but that protection is highly dependent on the status and whims of the ruler.
3. Cellarer: Someone has to keep track of how many eggs, pounds of flour, spoons, nails, bundles of wool and candles the castle has. Perhaps, in all the clutter (perfectly organized in their own mind, of course), they might have some important reference documents from the past or present.
4. Merchant with other hobbies: Many kinds of merchants — general outfitters, innkeepers, clothiers, jewelers, shipwrights, engineers — would have reason to accumulate lore about their favored subject areas. Not all are likely to be literate, but the most successful ones might be. And it’s not hard to pass off a manuscript about esoteric knowledge as part of your library of architectural knowledge.
5. Librarian of a trade post: People in isolated outposts of civilization are likely to want to preserve that civilization’s knowledge. Put that outpost somewhere on a major trade route, and the wisdom accumulated is likely to be a world-class trove. And such a place may well have someone in charge of keeping manuscripts and other knowledge organized; they are likely to speak many languages, and maybe read many more, both current and ancient. Getting to the trade post is sure to be a challenge.
6. Traveling peddler: An itinerant merchant could easily get away with carrying a strange mix of texts and other knick-knacks. That implies they only have as much material as they can carry, but it’s easy to fit a lot of knowledge into a few sheafs of pages — and easier still if combined with a sharp mind.
7. Sage as punishment: In a particularly anti-intellectual culture, someone might get saddled with the job of keeping the dangerous sources of knowledge isolated from the populace. This person might easily find themselves reading tomes of forbidden knowledge, having to (like the religious scholar) advocate the safety of the texts while at the same time publicly scorning them: “If we do not preserve the books of the Priests of Siros, how will we combat their pernicious arguments when they rear up again?”
8. Book seller with a private collection: A merchant may buy and sell books. But in a pre-printing press society, it seems unlikely that anyone would be able to either a) amass a very large personal collection or b) afford keeping books that are not for sale. But perhaps in a large, thriving city.
9. Leader of a religious minority: Someone tasked with leading or preserving the heritage of a minority group will often, of necessity, become a curator of its important knowledge. Perhaps they are the only one around who can read the Sacred Texts; perhaps they are the only one who can explain what the different beads on the Prayer Cycle mean.
10. Lexicographer/scribe/lawyer: If laws are complex and few people are literate, larger towns will start to have specialists whose job is to write up contracts, explain obligations, read letters and explain where to sign your X. These folks could easily end up accumulating large piles of valuable papers: old contracts that are still in effect but not currently enforced; historical documentation of border disputes; litanies of historical complaint against this or that merchant house.
11. Collegian: In prosperous cities, there may be actual colleges. They often begin as loose-knit associations of scholars, trying to pool resources and students. It takes quite a flourishing economy to support such a group.
12. Village healer: A small village or town will often have a person who knows Herblore, serving as the closest equivalent to a physician. This person will frequently accumulate other forms of knowledge as well. However, this position is always fraught: too little healing and the populace considers you a fraud; too much effectiveness, or effectiveness for the wrong person, and you may be considered a witch or worse.