According to tradition, a military marshal in the court of Henry IV of France presented some Carthusian monks with an alchemical manuscript for an elixir of long life. You can still buy the resulting concoction today.
I like a good origin story, and the origins of Chartreuse are a good story. Supposedly, it begins with a Marshall of Artillery in the French armed forces, François Annibal d’Estrées. He gave some Carthusian monks a recipe for an elixir in 1605 – although history declines to tell us where d’Estrées found it. Those monks brought the recipe to Carthusian order’s headquarters: the Grand Chartreuse monastery.
When the monks were expelled from their monastery in 1793 (part of the French Revolution’s war against Catholicism) the recipe came with them. The bearer was captured and sent to prison, where he passed it to a friend who sold it to a pharmacist. The recipe and the monks were reunited in the early 19th century, only to be expelled again in 1903 with another wave of French anti-religious sentiment. They moved to Spain and continued to produce Chartreuse there for a while, before finally returning to France.
The recipe remains a closely guarded secret today. Supposedly only two monks know all the ingredients, but it is said to include cinnamon, peppermint, thyme, lemon balm, hyssop, angelica, and over a hundred more herbs, flowers, and other secret ingredients.