Jonathan Archer's pet beagle, who travelled aboard Enterprise and became the crew's unofficial mascot.
Porthos was the beagle owned by Captain Jonathan Archer, who brought the dog with him aboard Enterprise for its mission of exploration. Archer was devoted to his pet, often sharing meals with him and taking him along on shore leave, and Porthos became a familiar presence for the crew and the ship's medical officer, Phlox.
The dog's most notable adventure came when he fell seriously ill after an away mission to a Kreetassan vessel, picking up an alien pathogen. Archer's frustration over the incident clouded his judgement while he tried to repair relations with the offended Kreetassans, and he was forced to make an embarrassing apology to them while Phlox treated Porthos in sickbay.
Porthos remained with Archer throughout the ship's voyages. His presence highlighted the more personal, homely side of Enterprise's crew and the series' interest in the everyday life of humanity's first deep space explorers. He is one of the best known animals in Star Trek.