D’Artagnan, the fourth Musketeer who gives to the title of Dumas’ novel a mystical, even metaphysical dimension, is indeed the captain of the elite guard here at the Court of Louis XIV.
The sequel to The Three Musketeers, The Twenty and then Ten Years After, is far more factual than the first book: Beginning from the days of the Frond, we actually can trace d’Artagnan’s career in and around the royal household. We don’t have too many details, but the few facts that we do have give us a strong idea that he was a special forces and a secret mission kind of guy. We also have a number of sources vouching for the integrity of his character.
For sure he was poor. When there was no action and no vacant positions available, d’Artagnan earned his living at Versailles by taking on some strange responsibilities — he guarded the royal menagerie and even the small dogs of Louis XIV. Yes, often his military rank did not correspond to the nature of the assignment; but he had an absolute trust of the cardinal and the king and to those two he owed all of his promotions.
Another interesting fact is that the paternal grandfather of Dumas’ protagonist was a successful merchant without any pretensions to nobility. This means that d’Artagnan took on his mother’s maiden name and de jure usurped the title. Years after the hero’s death, some audacious lawyer remembered this and decided to slap d’Artagnan’s grandson with a suit. But the name had already become a legend and the infuriated judge threw the case out, fining the petitioner instead.