The novel was written and published by Alexandre Dumas in 1844 and is the first in the d’Artagnan Romances. Three Musketeers follows D’Artagnan traveling to Paris to join the Musketeers of the Guard. Though he’s not able to join immediately, he becomes friends with three of the most formidable musketeers, Athos, Porthos, and Aramis.
The story is based on real people during Dumas's time. The encounter that happens to D'Artagnan on his visit to Treville, leading him to meet Athos, Porthos, and Aramis was real. The rest was made up from there.
D'Artagnan was Charles De Batz Castelmore d'Artagnan
Athos was Armand de Sillègue d’Athos d’Auteville
Porthos was Isaac de Porteau.
Aramis was Henri d’Aramitz.
Monsieur de Tréville was Jean-Arnaud du Peyrer de Troisvilles.
Full synopsis available via Utah Shakespeare Festival: https://www.bard.org/study-guides/synopsis-the-three-musketeers/