Nicolas Flamel
Flamel gained a reputation after his death in 1418 as an alchemist. He was wealthy, but his known sources of wealth seem to be enough to explain this. He married a wealthy widow, Perenelle, and in addition to his successful book selling business he invested widely in real estate and (according to some sources) lent money. The first recorded suggestions that he was an alchemist come nearly a century later. The series of books is the Harry Potter series, where he figures at Hogwarts as an ancient alchemist.