The Vulcans were a warp-capable humanoid species from the planet Vulcan in Star Trek. They were widely renowned for their strict adherence to logic and reason as well as their remarkable stoicism.
The Vulcans were once an extremely violent and emotional people. Paranoia and homicidal rage were common. As their level of technology increased, the Vulcans eventually reached a point where their violent nature threatened the extinction of their own species. In an effort to avoid this fate, a Vulcan named Surak developed a new philosophy, where emotions were to be controlled and repressed, with logic and reason to be their guidance in life.
Those who opposed harsh and emotionless logic left Vulcan and founded colonies elsewhere, most notably the Romulans.
The official First Contact between Vulcans and Humans came on April 5, 2063, when a Vulcan survey ship, the T'Plana-Hath, detected the warp flight of Zefram Cochrane's Phoenix.
In 2161, their homeworld became a founding member of the United Federation of Planets. By the 24th century, Vulcan remained one of the principal Federation members, and was deeply involved at all levels of that society.
Vulcans and many of the Milky Way's species all shared a common ancestry back to the Ancient Humanoids and the DNA code they produced and seeded across the galaxy. Though each evolved under separate conditions from each other, their shared DNA allowed these species to remain roughly compatible and viable with each other.