So the end note talks about how the Earl was modeled after a real-life person who called himself a "time traveling alchemist." I looked it up and the person the author is talking about is the Count of St. Germain. He had all these elaborate fake names, showed up in various countries, could speak dozens of languages, and made up crazy stories about his origins. To me, the Count seems like such an interesting figure because he achieved all this during the 1700s. It's amazing that he didn't die while traveling and that he was so educated in various arts, considering that there weren't a lot of resources dedicated to substantial learning.
So even after his supposed death in the late 1700s, there have been reports of how he's reappeared in different high-society events, up until the 20th century.