T'Les and her husband had met only once prior to their bonding and marriage. However, even though they were strangers at the time of their marriage, they grew to love and care for each other deeply. (ENT: "Home") In 2088, T'Les and her husband had their only child, a daughter named T'Pol who later became a sub-commander in the Vulcan High Command and was assigned to the NX-class starship Enterprise NX-01 in 2151. (ENT: "Zero Hour") T'Les became a widow when her husband, and T'Pol's father, died sometime prior to 2151. (ENT: "The Xindi")
In 2154, after returning from the Xindi incident, T'Pol visited her mother on Vulcan, and brought Commander Tucker without telling her mother beforehand. T'Les was not happy to see T'Pol with a Human companion, especially given that T'Pol had been engaged in a family-arranged bonding with a Vulcan named Koss. T'Pol had broken off the arrangement three years earlier, in order to stay aboard Enterprise. T'Les insisted, however, that T'Pol keep her marriage agreement with Koss. Despite her initial disdain towards Tucker, T'Les could not help but eventually like him. She was certain he was in love with her daughter. Able to sense a strong bond between them, T'Les hoped that Tucker would inform T'Pol of his feelings for her before she married Koss.
T'Les notified T'Pol that she had "retired" from her teaching position at the Science Academy. In reality, because of her daughter's actions on P'Jem in 2151, T'Les had been under investigation for removing classified material from the Science Academy, and had been forced into an early retirement due to the falsified charges. (ENT: "Home")
T'Les later joined a group of Vulcan dissidents known as Syrrannites, who were vulnerable to arrest after they supposedly destroyed the United Earth Embassy. After Archer and T'Pol were captured by the Syrrannites, T'Les came to their aid and persuaded T'Pau, the head of the movement, to trust them. T'Les advised T'Pol that the Vulcan High Command was corrupt and evil. She died in her daughter's arms when the High Command bombarded the Syrrannites' compound – the T'Karath Sanctuary in Vulcan's Forge. In her last moments, she expressed her pride in and love for her daughter and said that she had joined the Syrranites to find Surak's original writings, in part, to help T'Pol who had always struggled with her emotions. (ENT: "Awakening")
T'Les was played by actress Joanna Cassidy.
In the script for "Home", T'Les was introduced as "a dignified Vulcan woman on the low side of a hundred."
Joanna Cassidy was cast as T'Les while having a recurring part on the series Six Feet Under. The fact that the casting department at Star Trek: Enterprise shared duties with Six Feet Under helped her land the role of T'Les. Shortly after portraying the character, Cassidy stated, "I'm definitely mother material these days and I think that's why they thought of me for Star Trek: Enterprise. They asked me if I wanted to come in and play T'Les and I said yes [...] I was very pleased to be asked to be on the show." (Star Trek Magazine issue 120, p. 97) The introduction of T'Les may have also been influenced by an interest in adding some gravitas to the character of T'Pol. "They're testing Jolene Blalock's acting chops by giving her heavy stuff to play," reckoned Cassidy.
Thinking of T'Les as a welcome acting challenge, Joanna Cassidy tried to mentally unravel the character's motivations. "I saw her as an extremely confident woman," reflected the actress, "but secretive [....] Not forthcoming might be a better description. She's very strong. Her past wasn't really spoken of, but I assume she lost her husband. I sort of filled in the spaces [...] And I think she's filled with a great passion and love for her daughter which would enable her to have such feelings of somewhat being abandoned. My sense was that T'Les felt abandoned and wanted her daughter involved in her life again."
The insights that the series did offer into the relationship between T'Les and her daughter made an impression on Joanna Cassidy. "My understanding was that on Star Trek you hadn't really seen any Vulcan mother-daughter relationship before, but I wish they'd brought it in earlier," Cassidy remarked. "I think it could have been a very interesting part of the series and it could have crossed over into something about the Vulcans that people haven't learned yet."
Joanna Cassidy found that assuming the role of T'Les for the episode "Home" was very enjoyable but involved a few difficulties, not the least of which was adopting the reservedness associated with the part. "T'Les is such a stoic and unemotional person, and I am not a stoic and unemotional person. I'm very animated," explained Cassidy. "So to hold myself back physically and emotionally was a real challenge." (Star Trek Magazine issue 120, p. 97) The actress also commented, "I was doing slight smiles, and I was told that was not appropriate! Sometimes I even showed too much in the eyes. Vulcan feelings are very hidden. And I loved that. I'm very expressive, so to pull it all in was interesting." The make-up for the part was another restrictive challenge that Cassidy was faced with, though she was pleased with the prosthetics. "I was in a chair for a couple of hours and I had to rein myself in during that, too," she said. "But I loved the look. Once it was done I thought it was terrific. And I got to keep my ears. But I understand that they don't last, that they break down over time." (Star Trek Magazine issue 120, p. 97)
Returning to play T'Les in "Awakening" was somewhat easier for Cassidy. She later remembered, "I fitted in a little bit more, but it's still hard to get into the rhythm when you're not there every day. Still, I felt comfortable. I knew everyone. I knew what to expect. I knew what the make-up would be like." (Star Trek Magazine issue 120, p. 98)
The character of T'Les was killed off in "Awakening" because, among other reasons, Paramount Pictures couldn't afford to pay Joanna Cassidy to play her in "Kir'Shara". (Information from Mike Sussman) As evidenced by the final draft script of "Awakening", however, T'Les' death scene was added to with some additional dialogue for the final version of the scene. For example, in unscripted lines of dialogue, T'Les discovers T'Pol has successfully helped find the Kir'Shara and tells T'Pol, "You have always struggled so with your emotions. I came here, I did all this to help you." Other lines that weren't scripted include T'Les reassuring T'Pol that she would understand what her mother had meant by that, and T'Les affectionately referring to her daughter as "my T'Pol."
Cassidy was very surprised to learn of T'Les' demise and suspected the same was true of T'Pol actress Jolene Blalock. "I hadn't read the scripts between 'Home' and 'Awakening', so I didn't know how they were leading up to 'Awakening'," said Cassidy, "but it was probably as big a shock to me as it was to Jolene to get a mother and to lose a mother. We had such a nice time together. I think she was disappointed to lose me. I think having my character there opened a side of her that hadn't really been tapped." (Star Trek Magazine issue 120, p. 98)