D'Artagnan was a beagle dog living in the 22nd century. Named after a musketeer from the Alexandre Dumas novel The Three Musketeers, he was the brother of Jonathan Archer's Porthos. He had two other brothers, named Aramis and Athos. D'Artagnan and his brothers were born to a female dog owned by the mother of one of Archer's ex-girlfriends. (ENT: "A Night in Sickbay")