Legendary alchemist/diplomat/con-man/musician/Illuminatus/liar/mystery. Born approximately 1710 and died in 1784.

Saint-Germain first came to prominence when he appeared at the court of Louis XV of France. He told everyone that his name was "Comte de Saint-Germain", that he had great alchemical powers, and that he was able to repair flawed diamonds. Louis liked him (and his diamonds), and he sent Saint-Germain on a secret peace mission to Holland and England. However, the English captured him and deported him to the Austrian Netherlands. After that, he spent the rest of his life traveling Europe, going from one royal court to another.

And still, no one really knows who he was. It has been theorized that he was a jeweler's son from Bohemia or Hungary who made up stories of his mystical prowess in order to sell his diamond coloring techniques (and, not coincidentally, gave him the opportunity to con money and acclaim from the wealthiest families in Europe).

Saint-Germain had other useful talents besides grifting. He was a talented musician and composer -- his compositions have been compared to those of Handel, Telemann, and Gluck. He invented "Russian tea" -- a laxative used by the Russian Navy during a Meditarranean campaign. He developed dyeing techniques which allowed him to counterfeit gems. He was fluent in over a dozen languages, and his feats of memorization astounded the French court.

Of course, Saint-Germain's eccentricities also helped gain him fame. When he appeared in public, he dressed only in black and white. He liked to talk about history in the first person. A senile countess' recollection of seeing him (looking the same age) back in 1710 led him to claim to possess the Elixir of Youth. He traveled under a dizzying array of aliases. He claimed to be a lost prince of Transylvania.

And since his death, Saint-Germain's legend has only grown stronger. It's said by some that he was a Masonic secret master; that he taught Mesmer, Swedenborg, and Cagliostro; that he helped put Catherine the Great on the Russian throne; that he conspired against George II of England; that he designed the flag and seal of the United States; that he caused the French Revolution; that he was the prophet Samuel; that he was an 18th dynasty High Priest of Ra; that he was St. Alban; that he was Merlin; that he was Roger Bacon; that he was Tsong-ka-pa (the founder of Yellow Hat Buddhism); that he was Christian Rosenkreutz; that he was Janos Hunyadi, a Transylvanian hero; that he was Christopher Columbus; that he was Sir Francis Bacon; that he was Marcel Duchamp; that he was a vampire; that he's still alive today, manipulating events behind the scenes and creating collaboratively-filtered databases...

Research from GURPS Who's Who 2, compiled by Phil Masters, "Le Comte de Saint-Germain" by Kenneth Hite, pp. 70-71.

Lord of Nothings reminds me that Saint-Germain is also an important and immortal "plot device/secret leader/general badass" in the Unknown Armies roleplaying game.