The Romulans are a militaristic race closely related to the Vulcans. Unlike the Klingons, Romulans are more concerned with conquest than honor on the battlefield, and frequently use deception and subterfuge to further their aims. Of the major powers, they are the first known to perfect the cloaking device.
The ancestors of the Romulans left the Vulcan homeworld while the planet was still in it's more violent times. They remain physically close to Vulcans in appearance, though are not as strong as the world they settled, called Romulus by the Federation, has a gravity closer to Earth than Vulcan. They are ruled by a totalitarian military government that demands total loyalty of its subjects. Duty to the Empire counts above everything, including a Romulan's own life. This is not considered a great loss to individual Romulans as they don't have much of a life.
Curiously, many Romulan names are very similar to the ancient Roman Empire on Earth. Soldiers are called "Centurions," both had a "Senate," both societies were militaristic and intent on conquest and expansion, and the name "Romulan" sounds close to Roman. The Romulans insist this is simply a coincidence.
They were encountered by Earth and Vulcan ships before the Federation, but unlike the Klingons they remained a mystery. Romulan society is xenophobic, and until recently would have nothing to do with outsiders. Highly territorial and isolationistic, they shunned contact and would not permit others' ships to stray in. For whatever reason, the Vulcans' highly mathematical minds could not make the connection between the Romulans' language and their own. The few transmissions picked up were audio only, no pictures. This was thought to be part of the Romulan drive to keep as much of themselves a secret as possible. It turned out no one among them knew how to build and repair a TV camera.
The Federation fought an inconclusive war with the Romulans early in its history, and the peace treaty set up a Neutral Zone between the two powers. Things were quiet between the two powers for decades before a Romulan Warbird destroyed several Federation outposts before it was tracked down by the Enterprise under Kirk and destroyed. It was suspected they were testing Federation defenses. But later on, a Romulan historian admitted, "We were bored."
Romulan symbol used in early 23rd Century
Shortly afterwards, the Romulans signed a technological exchange treaty with the Klingons. The Romulans acquired Klingon-design ships (which were fitted with Romulan toilets as the old Federation joke had spread to them) in return for cloaking technology. Despite that the Klingons were always holding to their part of the alliance, the Romulans surprised them with a sneak attack. They would remain blood enemies until the Dominion War. The Klingons called it a dishonorable backstab, taking advantage of a border they only lightly picketed due to the alliance. The Romulans countered the latest batch of ships the Klingons sold them were useless as what passed for a waste disposal system had broken, and their intended crews had died after inhaling the smell.
Peace between the Federation and Romulans was an uneasy one, pockmarked by numerous border skirmishes. Then the border was silent for well over a decade, interrupted only when a Borg vessel destroyed outposts on both sides of the Neutral Zone. The Romulans stated they were drawn away from the Galactic scene by "internal matters." It had been thought they were talking about civil conflict. Instead, the government was trying to track down and destroy a batch of "Barney" tapes that had somehow been smuggled into the Empire.
About two decades ago, the Romulan beauracracy suffered a devastating loss of data. It was originally thought to be a computer virus. It was since revealed they had never bothered to have their clerks put numerous paper records in their computer files, and a Federation agent destroyed hundreds of years worth by means yet to be revealed.
The Borg attacks left Romulans wondering about which direction their society should go. Should they try and remain isolated to protect their "perfect society," or should they communicate and trade with others, hoping for some fresh ideas? A trip to Romulus by Spock suggested the latter as he came across an underground interest by many in Vulcan ways and philosophy. Only a fraction truly wanted to follow Surak's teachings though, "We just want to learn that cool nerve pinch."
Still, the old xenophobic shell is cracking as Romulan refugees and military defectors, the latter once extremely rare, become more and more common. Captain Treki under the USS Freedom - D once escorted a defecting Romulan starship from the Neutral Zone to the nearest Federation starbase.
Commander Lera t'Resan of the USS Freedom is Romulan.
"And she's cuuuuuuuuuute." :-D
"Yes Lera, they know." 9.9