Valeris is a vulcan assassian
As a child she and her mother were abducted by renegade Klingons as part of a plot to seize a border world. When her father refused to negotiate the Klingons killed several people in front of her eyes and severely injured her mother. Valeris and the remaining hostages were rescued by a Starfleet team from the USS Ark Royal commanded by then Captain Lance Cartwright, but the trauma fostered a deep hatred and mistrust of the Klingons. Valeris convinced herself that her feelings towards the Klingons were logical and based in reason.
As a student at Starfleet Academy Valeris wrote a paper outlining a case against pursuing peaceful relations with the Klingons. By then an Admiral, Cartwright learned of the paper and had Valeris summoned to his office at Starfleet Headquarters. There he convinced her to delete the paper before it became public knowledge and damaged her career potential. At that meeting Cartwright revealed that he felt as she did about the Klingons. In the years that followed she would serve as an agent for Cartwright as he pursued his own agenda.
Early in her Starfleet career, Valeris became a protégé of Captain Spock. Lt. Saavik, who felt that Valeris was bigoted and arrogant nevertheless gave a full recommendation for Valeris out of her loyalty to Spock. However Saavik's conflicted feelings over recommending Valeris caused a rift to develop between Spock and Saavik, and Saavik transferred off the Enterprise at that point.
Following the destruction of the key Klingon energy production center of Praxis, Valeris became part of the conspiracy of Klingon, Federation, and Romulan individuals who stood to lose should the Klingons sue for peace.
Valeris was placed on board the USS Enterprise (NCC-1701-A) with two others, Yeomans Burke and Sammo. Encountering Captains Kirk and Spock, she explained that she was informed the Enterprise needed a helmsman so she volunteered. She spent the time between leaving spacedock and the initial meeting with Chancellor Gorkon's ship planting programming in the ship's computer and moving supplies around to prepare for the boarding of Gorkon's ship. When she learned that Captain James T. Kirk had expressed his own dislike for the Klingons in a personal log she made sure to make a copy of the log as she felt it would be useful later.
After Gorkon's ship was boarded instead of fighting it out with the Klingons as Valeris expected Kirk instead went to offer aid to the Klingons. Doctor Leonard McCoy went with him, and when McCoy could not save the chancellor the pair was arrested by General Chang - himself another conspirator. In the following trial the log Valeris made a copy of was provided to the Klingons, and Change made great use of the log in the trial.
Kirk and McCoy were eventually rescued. Realizing that Burke and Samno could expose her and the others Valeris murdered the two men with a phaser set at stun at close range. Encountering the bodies of the two men Kirk pieced it all together and realized that Valeris was the traitor. At Kirk's orders Spock entered into a mind meld with Valeris and dragged the rest of the conspiracy into the light.
General Chang attacked the Enterprise after the ship arrived at Khitomer, however using a modified torpedo the Enterprise crew was able to defeat him and destroy his ship. The senior staff beamed down in time to prevent the death of the Federation President. Spock beamed down with Valeris, and presented her to the gathered officials. McCoy announced they had a full confession from her.
Following the return of the Enterprise to Earth Valeris was sentenced to life imprisonment on Jaros II. She proved resistant to rehabilitation while on the colony - despite the efforts of the prison psychologist and covert Section 31 agent to draw her out. After the death of Lance Cartwright in 2298 Valeris was the only known survivor of the conspiracy.
Valeris was recruited in 2300 to assist with a Starfleet intelligence operation to prevent Kriosian terrorists from destroying Qo'noS. During this operation Klingon intelligence agent Kaj penetrated the shell Valeris had drawn around herself and Valeris was finally able to put her hatred of the Klingons behind her. For her role in preventing the destruction of Qo'noS Valeris was given her freedom and a new identity. As T'leris she became a civilian pilot on a Vulcan colony.
Played by actress Kim Cattrall. See also Martia (Star Trek VI:The Undiscovered Country)