Sela

Commander Sela was an officer in the Romulan military, and an extremely important figure in the Empire's covert attempts to destabilize both the Federation and the Klingon Empire. She was the product of a union between Starfleet officer Tasha Yar's counterpart from an alternate timeline and a Romulan general.

Events leading to birth
In the year 2344, while in the middle of a battle with four Romulan Warbirds, the USS Enterprise-C traveled through a temporal rift to the year 2366. This had the effect of creating an alternate timeline, wherein the Federation was at war with the Klingon Empire, and Tasha Yar had not died at Vagra II.

Emerging from the rift, the Enterprise-C encountered its successor, the USS Enterprise-D. Through Guinan, the Enterprise-D crew learned that, in order for the timeline to be restored, the Enterprise-C must return through the rift, even though doing so would almost certainly mean their deaths. Learning from Guinan that, in the other timeline, she had died a meaningless death, Tasha requested and was granted a transfer to the Enterprise-C, which returned through the rift and resumed the battle with the Romulans

Early life
While the Enterprise-C was destroyed, several crewmembers survived and were taken prisoner by the Romulans, Tasha among them. After being interrogated, all of the survivors were to be executed, but a Romulan general became enamored of Tasha, and offered to spare the lives of the prisoners if she became his consort, a condition to which Tasha agreed. One year later, she gave birth to a daughter, Sela. When Sela was four years old, Tasha took her and attempted to escape, but sensing that her mother was attempting to take her away from her home and her father, Sela cried out, and Tasha was discovered and subsequently executed.

Military career
Over the next eighteen years, Sela rose through the ranks of the Romulan military, achieving the rank of commander. In that capacity, she was a major player in plots to disrupt the alliance between the Federation and the Klingon Empire, one of which involved kidnapping Starfleet officer Geordi La Forge, and brainwashing him to kill Klingon governor Vagh. (TNG: "The Mind's Eye") She was also involved in lending support to the House of Duras in their attempt to gain control of the Klingon Empire, ferrying them materials and supplies in cloakedRomulan vessels. Sela was foiled, however, when Captain Jean-Luc Picard led Starfleet to the Klingon-Romulan border and instituted a tachyon detection grid, making it impossible for any cloaked ship to cross the border undetected. Data, in command of the USS Sutherland, managed to use the tachyon signature that formed around Sela's ships, and ordering three photon torpedoes, lit up the tachyon field around the three cloaked Romulan Warbirds, causing them to reveal themselves, forcing Sela to withdraw back to Romulan space, causing the House of Duras to lose the civil war. (TNG: "Redemption", "Redemption II")

Sela was encountered again in 2368, when she masterminded a plot to invade Vulcan, exploiting AmbassadorSpock's underground reunification movement on Romulus. Using three stolen Vulcan ships carrying a Romulan invasion force, she attempted to use Spock to convince the Federation that a peace envoy was en route to Vulcan. Spock refused, however, forcing Sela to use a preprogrammed hologram of Spock as an alternative. She then made the mistake of leaving Spock alone with Picard and Data, the latter having become proficient with Romulan computer systems. When Sela returned to her captives, she was captured instead and was forced to watch as Data foiled her plot by warning the Federation, forcing the cloaked warbird escorting the stolen Vulcan ships to destroy them rather than let them be captured, before the android used a Vulcan nerve pinch on Sela, knocking her out.