T'Plana Hath was a philosopher in Ancient Vulcan history who (presumably) carried on the work of Surak and became one of the founding figures in modern Vulcan Philosophy.
Years later, the Vulcan High Command would name several vessels after the philosopher in homage.
Two ships were known to carry her name. The first was designated T'Plana-Hath, which was presumably a landing shuttle of a larger Vulcan vessel in Earth orbit. The T'Plana-Hath shuttle landed in Montana on April 4, 2063 to make first contact with mankind after detecting Zefram Cochrane's warp signature (Star Trek: First Contact).
Another vessel by the name of T'Plana was lost with all hands in a class-5 neutronic storm in the 21st Century (ENT: "The Catwalk").
Mentioned in Star Trek IV: The Voyage Home as Spock was retraining his mental abilities on his home computer. He referred to T'Planna Hath as "the founder of modern Vulcan Philosophy."