Romulans are an offspring species of the Vulcans that emigrated to the planet Romulus ca. 2000 years ago. Romulans are extremely talented at subterfuge, making their use of cloaking devices unparalleled and their damage bonus from de-cloaking higher than that of other species. Additionally, Romulans' Vulcan heritage is reflected in their immense physical strength, making them powerful melee combatants. After a failed coup d'état in 2379 and the destruction of Romulus in 2387, different factions formed among the surviving Romulans.
As of 2409, two major Romulan factions exist:
- Romulan Republic, led by the reunificationist Proconsul D'Tan, is a playable faction based on New Romulus, or "Mol'Rihan". The Republic cooperates with the Reman Resistance and is supported by the United Federation of Planets as well as the Klingon Empire.
- Romulan Star Empire (or, as its detractors might say, what's left of the Empire), with its capital Rihan on Rator III, is ruled by Empress Sela and controlled by the oppressive Tal Shiar. Sela has also enlisted the help of Hirogen Hunters and Cardassians of the True Way to strengthen her rule. Moreover, the Star Empire cooperates with the mysterious Elachi and is rumored to be secretly influnced by the Iconians.
 Physical appearance
Romulans have pointed ears, upswept eyebrows, and copper-based blood that is green when oxygenated in the arteries and copper or rust colored when deoxygenated in the veins. The Romulan heart is said to be gray, though this may simply be poetic imagery. Many Romulans have a V-shaped ridge above the bridge of their nose, which was not shown in TOS, but introduced in the later series and films. Like Vulcans, Romulans are almost always depicted as having dark or black hair, though brown-haired examples have also been seen in various media, and STO includes rare examples of blonde Romulans, usually women.
Romulans share the longevity common to their Vulcan cousins. In "Unification", the Romulan Senator Pardek shared a friendship with Ambassador Spock lasting at least 80 years. Romulans also have in common Vulcans' greater physical strength than that of a Human. However, the similarities end when it comes to Vulcans' mental abilities, which the Romulans do not share.
 Other information
The Romulans began as a revolutionary group of Vulcans, who were referenced as "those who march beneath the Raptor's wings" and refused to accept the Vulcan philosopher Surak's teachings of complete suppression of emotions. Around AD 400, the dissident group split off from Vulcan society and began the long journey to the planets Romulus and Remus.
The Romulans are of the Vulcan species. One of three theories regarding how the Romulans arrived at the stellar system that includes the planets Romulus and Remus involves Sargon's people, referred to in conjecture as the "Arretians", as mentioned in the Star Trek: The Original Series (TOS) episode "Return to Tomorrow". Sargon claimed that his people had seeded their species throughout the galaxy, and Spock said that could explain some enigmas of Vulcan pre-history. Hanoch, one of Sargon's people and a rival, further claimed that Spock's hybrid Human-Vulcan body was a "good fit" for his alien physiology. If these claims are true, then the Arretians may have been the antecedents for the Romulans — and indeed, they may have also been the species known as the Preservers. The inhabitants of Mintaka III ("Who Watches The Watchers?") seem to support this theory.
Another theory says that Vulcan colonization efforts led to a split, or schism, between factions favoring the school of logic espoused by the philosopher Surak and opposition groups, led by S'task, which ended up leaving Vulcan. However, there is no explicit canon evidence that the group which left Vulcan was in rebellion against Surak. The "Vulcan Soul" Trilogy, written by Josepha Sherman and Susan Shwartz, told the story that it was Surak's idea that some of the Vulcan population should leave their homeworld to find a new home so that the Vulcan race could be preserved due to the endless wars then raging on the homeworld. (Conversely, the Star Trek: Enterprise episode "Awakening" includes a line from the long-deceased Surak referring to the enemies of logic in his time as "those who marched beneath the raptor's wing": this would appear to be a reference to the symbol of the Romulan Empire.) These Vulcans arrived on Romulus and founded what would become the Romulan Star Empire. This theory is supported by a reference within the Star Trek: Enterprise episode "United": Senator Vrax refers to Vulcans as "our distant brothers" during the first part of the episode.
Information from "Balance Of Terror" suggests yet a different theory. While Spock makes it clear that the events during the period of Surak are well documented ("The Savage Curtain"), he is completely uncertain in regard to the origin of the Romulans: "If the Romulans are an offshoot of my Vulcan blood – and I think this likely – then attack becomes even more imperative. Vulcan, like Earth, had its aggressive, colonizing period, and if they have retained that martial philosophy… then weakness is something we dare not show."
- Species trait: Romulans are extremely talented at Subterfuge, making their use of Cloaking Devices unparalleled and their damage bonus from de-cloaking higher than that of other species. Additionally, Romulans' Vulcan heritage is reflected in their immense physical strength, making them powerful melee combatants.
- In Space: +Stealth while Cloaking, Bonus damage when exiting Cloak
- On Ground: Bonus Physical Damage, chance to knock down foes when using Melee attacks.
 Duty officers
- Romulan at Memory Alpha, the Star Trek Wiki.
- Romulan at Starbase UGC, the user-generated-content Wiki for STO.