Sub-Commander T'Rul was a Romulan officer temporarily assigned to the USS Defiant, in 2371, to operate and guard a cloaking device her government had loaned to the Federation for covert exploration of the Gamma Quadrant.
Several hours after the Defiant entered the Gamma Quadrant, the starship (or at least its subspace variance) was detected by two Jem'Hadar attack ships. T'Rul was aware of this phenomenon that had been a closely guarded Romulan secret. On her advice, the ship dropped out of warp. After the Dominion ships began sweeping the area with an anti-proton scan, T'Rul admitted that she was unsure if it could penetrate the cloak.
Some time later, after the Defiant was boarded by the Jem'Hadar, T'Rul was able to kill one of the invaders using her disruptor. After doing so, she was injured by another Jem'Hadar soldier. (DS9: "The Search, Part I")
Along with other members of the Defiant, T'Rul was taken to the Founders' homeworld and placed in Borath's elaborate simulation of Dominion treaty negotiations with the Starfleet officers. During the simulation, she was incensed that the Romulan government had been excluded from the peace talks and threatened war.
T'Rul was played by Martha Hackett.
She was the first Romulan character to appear in Star Trek: Deep Space Nine, and was not seen again after the two-parter which introduced her.
T'Rul re-appears in the Prophecy and Change story "The Devil You Know". In 2374, she was assigned to Project Blue Sky, a combined Federation-Romulan scientific think tank. In the non-canon story, she recounts how her husband and two children were part of a diplomatic delegation on Cardassia Prime at the time the Romulan Empire declared war on the Dominion. A transmission intercepted by Starfleet Intelligence revealed they were among several Romulans executed by the Dominion.