Romulans are a humanoid species from the planet Romulus. Long ago, the Romulans were Vulcans who disagreed when the Vulcan leader Surak started preaching logic and self-control. They left Vulcan and found the twin planets of Romulus and Remus; founding the Romulan Star Empire. Romulans are physically stronger and more resistant to radiation and toxicity than humans and comparable to Vulcans, though seem to lack the Psionic capabilities of Vulcans.
Romulans, unlike Vulcans, are just as emotive as humans, and their culture is extremely xenophobic and insular - the Romulan Empire before it's fracture was essentially a police state. Romulans are often seen by other species as deceitful and untrustworthy. Romulans were the first race to develop cloaking devices, having them as early as the 22nd Century. They later sold the technology to the Klingons during a short-lived alliance, however Romulan cloaks remain slightly more advanced. Although general xenophobia is common among Romulans, they have a racial enmity with Klingons, Vulcans and once considered the Remans little more than slaves. Romulan ale is a popular beverage in the Federation although it is technically illegal.