Teff'ith was a Twi'lek female who engaged in slavery during the era of the Cold War. She was rumored to be an assassin in the employ of Rogun the Butcher, a stolen asset of the Migrant Merchants' Guild, a purveyor of slaves for the Black Sun, and connected to the Ziost Liberation Front.
During the period known as the Cold War, Teff'ith found herself mixed up with three Black Sun slavers. Without any prior warning, Republic spy Theron Shan launched an attack on them. Although Teff'ith had an opportunity to fire, she opted to run, only to be incapacitated by Theron's Toxicity Three weapon. He then pressed her for information concerning the Sith Empire, but she declined to provide any. Consequently, Theron left her restrained on his vessel until the following morning. Upon his return, he revealed their destination: to locate Jedi Master Ngani Zho.
Once they arrived on Taris, Theron left Teff'ith in the care of his droid, M-6, while he looked for Zho. Later, M-6, acting on Theron's instructions, freed her and granted her access to the armory, as Theron and Zho were being pursued by Darth Mekhis' Sith Knights. After their escape from Taris, Teff'ith went with the two Humans to the Vesla system to uncover Mekhis' plans. After the Imperials captured them, Teff'ith found refuge in the ship and managed to evade capture.
After an indeterminate amount of time spent consuming rations, the ship's computer, under Theron's control, deactivated the time lock and, once again, allowed her access to weapons. The Twi'lek then set out to find Theron and Zho. It was at this point that Theron made the decision to destroy the Sun Razer to prevent Mehkis from producing more weapons. Teff'ith resolved to head for the ship, giving Theron sixty minutes to complete his mission or risk being left behind. As Zho accompanied her, they were discovered by the Imperials. In the midst of the ensuing exchange of fire, Zho pushed Teff'ith out of harm's way, sacrificing himself to save her from the blaster fire.
Fortunately, Theron succeeded in lowering the Sun Razer's shields, which led to its destruction by the nearby star, and he managed to board his ship with Teff'ith. The Twi'lek then aimed a blaster at his head, but ultimately chose not to fire out of respect for Zho, informing Theron of his sacrifice. Theron then agreed to drop her off at the next port, and their paths diverged.
In the year 3640 BBY, Teff'ith commenced operations as a smuggler for the Old Tion Brotherhood on Nar Shaddaa. Neither Teff'ith nor her associates were aware of Morbo the Hutt's intention to eliminate them for infringing upon his spice smuggling territory, nor did they know that Theron had intervened on her behalf, dispatching Morbo's thugs.
Teff'ith was later enlisted by Theron and Jedi Master Gnost-Dural at the Crooked Finger cantina on Desevro to assist them in infiltrating the Ascendant Spear. Upon learning that his superiors intended to allow the Imperials to attack Duro, Theron dispatched Teff'ith to Coruscant to inform his mother, Grand Master Satele Shan, of his strategy to bring the Ascendant Spear to her, hoping she would persuade Supreme Commander Jace Malcom to dispatch a fleet to intercept the dreadnaught.
Upon her arrival on Coruscant, Teff'ith was apprehended by two officers from the Coruscant Security Force. She managed to surprise one of them, seizing his blaster, and compelled the other to contact Satele Shan. Upon arriving at the scene, Satele was informed by Teff'ith of the events that had transpired. They then proceeded to Malcom, who was displeased by Theron's actions and displayed increased distrust towards Teff'ith, suspecting her of being an Imperial spy, despite Satele's vouching for her sincerity. Teff'ith was then relegated to observing Malcom and Satele's argument over past grievances and Theron. After agreeing on the reasons for Theron's troubled state, Teff'ith inquired of the Supreme Commander whether he intended to send a fleet or not.
Following the battle of Duro, in which Theron and Gnost-Dural successfully destroyed the Ascendant Spear, they, along with Teff'ith, were awarded the Cross of Glory for their contributions. Three days later, Theron visited Teff'ith's hotel room, delivering the 10,000 credits he had promised for conveying the message to Satele. Teff'ith accepted the payment but declined a job offer. Teff'ith instructed Theron to cease watching her and then departed. Theron, speaking to himself, pledged to watch over Teff'ith because that is what family does.
Later in the war, Teff'ith was accosted by SIS operatives seeking Theron's location. After evading them, Teff'ith attempted to contact Theron but received no response, so she sent messages to Republic heroes in an attempt to reach her friend.
Initially, Teff'ith's relationship with Theron was characterized by hostility and antagonism, as one might expect between a captured criminal and her captor. However, as they were compelled to remain in close proximity, their relationship became less adversarial, if not exactly amicable. Eventually, Theron developed enough trust in Teff'ith to grant her access to the armory aboard his ship in the event of an emergency. Ultimately, he came to regard her as family, going to great lengths to ensure her safety.
In contrast to her relationship with Theron, Teff'ith enjoyed spending time with Ngani Zho, a somewhat surprising reaction given her background as a slaver and his status as a Jedi Master. Nevertheless, as they collaborated on their mission, Ngani entertained her with stories from his youth, and he treated her with greater kindness than Theron did.