The Story of Tahm Kench
Tahm Kench is an ancient demon — one of the oldest beings in Runeterra's river systems, a creature of pure greed and appetite that has existed since before the current civilizations' oldest records. He travels the waterways of Runeterra offering deals: he can grant wishes, solve problems, provide what people want, and what he takes in return is something less tangible than gold. He feeds on misery, specifically the misery of people who got what they wanted and discovered it cost them more than they knew.
His deals are not technically dishonest. He never lies about the terms. He is simply very good at offering what someone genuinely wants at a moment when they genuinely want it, and very good at structuring the transaction so that what they pay — in degradation, in loss, in the slow erasure of what made them who they were — isn't visible until the payment is already made. He is a connoisseur of the specific misery that follows fulfilled desire. He has refined his craft over a very long time.
He is present wherever human need is acute and unscrupulous offers are welcome: gambling dens, desperate docklands, courts where ambition has outrun ethics. He is charming, patient, and genuinely delighted by the variety of things humans want badly enough to accept help from something they know they shouldn't trust. He does not force anyone. The hunger is always theirs. He simply shows them where to direct it. The meal he serves is always the one they ordered.