T'Pol was a Vulcan who served aboard Enterprise NX-01 in the mid-22nd century. She was the first Vulcan to serve aboard a Human ship for any substantial period.
The Vulcan High Command assigned Sub-Commander T'Pol to the United Earth Starfleet vessel Enterprise in April 2151 following Earth's accidental first contact with the Klingon courier Klaang. She acted as "chaperone", in exchange for the Vulcan star charts and Klingon linguistic database, and was not immediately accepted by the Human crew. The ship's Chief Engineer, Commander Charles Tucker III, referred to T'Pol as a "spy". Despite the crew's misgivings, she was instrumental in uncovering a plot by the Suliban Cabal to destabilize the Klingon Empire. T'Pol was persuaded by Captain Archer to remain aboard following the successful conclusion of the mission to return Klaang to his people, instead of returning to the Vulcan Consulate in San Francisco.
Following the Xindi attack on Earth on April 24, 2153, Enterprise was recalled home and underwent a major refit in preparation for a mission into the Delphic Expanse. Since this mission was seen by the Vulcan High Command as being an Earth matter, Ambassador Soval ordered T'Pol to return to Vulcan to be reassigned to the Ministry of Information. It was expected that, after a brief time at the Ministry, she would be allowed to return to Earth to continue her diplomatic duties. However, T'Pol resisted. As Enterprise set course for Vulcan to deliver T'Pol home and proceed to the Expanse, she abruptly resigned her commission and chose to remain aboard.