Linea was a megalomaniac, unstable, unethical scientific genius and mass murderer, known throughout the galaxy as the Destroyer of Worlds. Extremely intelligent, she developed a pathogen that wiped out an enormous number of her people. She was sent to the prison colony Hadante for her crimes, and was even feared by the other prisoners there. She remained on Hadante until SG-1, who were unjustly convicted of a crime, arrived. She reappeared to SG-1 a year later, as her younger self under the guise as Ke'ra on the planet Vyus. (SG1: "Prisoners", "Past and Present")
SG-1 was on a mission to the planet of the Taldor, (which means "Justice"), when they were approached by Roshure, a criminal who was fleeing for his life. The unseen, yet powerful, Taldor beamed this prisoner and SG-1 to a courtroom where they were all sentenced to life on the prison planet Hadante. Upon SG-1's arrival, the team immediately went to work trying to figure a way out of the prison, something Dr. Daniel Jackson equated with Botany Bay. It was quite evident to Colonel Jack O'Neill and Teal'c that they needed to protect the two younger members of their team, since life in prison can be very cruel on ones so innocent. When one of the male prisoners made an advance toward Captain Samantha Carter, she was saved by Linea, who held considerable influence over all of the men of the prison (Linea appearing to be the only female prisoner at the time SG-1 arrived). Linea announced that Carter was under her protection and the rest of the prisoners backed off.
Jack and Carter met with Linea to discuss finding a source of power for them to use on the Stargate. If they could find a power source, they could free the inner ring of the Stargate and dial out manually. Linea was a scientist and she had developed chemically-induced cold fusion activators from some of the local plant life. Jack and Carter asked that she use this chemical fusion to help them escape and in return for her help, they'd take her with them, and win her freedom.
Linea took Carter under her wing and told her about how she ended up at Hadante. She said that she had attempted to cure a disease, but her work backfired and accelerated the disease instead of stopping it. Linea also warned Carter that the men of SG-1 were in danger because the leader, Vishnoor, would challenge them to maintain his position of authority. When Daniel tried to prevent some of the prisoners from killing themselves in the unstable vortex of an incoming wormhole, the prisoners believing that they were gaining freedom but in actuality dying as a result, Vishnor attacked him. Linea used a small device she held in the palm of her hand and killed Vishnoor, but everyone thought that Daniel had been the victor. Linea gave Daniel medication to help him recover from the strangulation and it was soon thereafter that he recalled the gate address of SG-3's next mission and he suggested going there to rendezvous with them and use their GDO to get home. Linea's power source was ready and the team along with Linea managed to escape and flee towards the Stargate.
During their escape, another prisoner named Simian met up with them and escaped along with them. He had been helped by Linea upon his arrival. She saw that he was blind and placed drops in his eyes and his vision was restored. Upon seeing her face, he ran in fear from her, not thanking her for restoring his sight. SG-1 then dialed the planet SG-3 were located on and they hitched a ride back to Earth at Stargate Command along with Linea, using their GDO.
SG-3 discovered Simian near their camp and took him to the SGC. There, Simian told them that Linea was the "Destroyer of Worlds", a megalomaniac genius, who conquered and destroyed numerous worlds throughout the galaxy, and was responsible for creating a pathogen that wiped out an enormous number of her people, the same pathogen which killed half the population of his homeworld before she was caught.
While on Earth, she learned that the Stargates can travel to thousands of worlds, and forcibly left the SGC after programming the base computer to indicate that it was about to self-destruct the base. She left a message on the computer screen in the control room after making her escape: "Thank you for your kindness. All debts have now been paid." Linea provided the chemical formula for her activators and then used her access to the computer system to make her escape. (SG1: "Prisoners")
Because of her brilliant hacking into their computer system, Stargate Command did not know to where Linea escaped. About a year later, SG-1 were on a mission to the planet Vyus, where they met a human population which was suffering from mass amnesia whom which the Vyuns called the Vorlix. They were taken to meet Ke'ra, the Minister of Health, Science and Restructuring in the Vyus Transitional Government. Ke'ra was the one everyone turned to for help when they needed medicine, since she was an accomplished apothecary.
Ke'ra immediately accepted SG-1's offer to help them figure out what caused the Vorlix, the name they gave to the event which took everyone's memories from them. Ke'ra thought that the event might have been linked to Dargol, a pesticide known for its harmful effects on the population's fertility and had environmental impacts similar to DDT and was banned as a result. Dr. Janet Fraiser asked that some of the Vyans go with her to the SGC where she could use her more advanced medical equipment to determine the cause of the amnesia. Two Vyuns, Orner and Mayris, accompanied Ke'ra to the SGC.
Dr. Daniel Jackson and Ke'ra were strongly attracted to each other. Having just lost Sha're, Daniel was very cautious about his behavior, but he couldn't help but be taken in by Ke'ra's open personality and brilliant mind. Daniel continued to show her the facility and kept her company.
Major Samantha Carter continued to study Linea's research diary which had been discovered in the library on Vyus. While Fraiser worked on a cure, Carter figured out what had caused the Vorlix, and she soon came to the conclusion, despite Colonel Jack O'Neill's reluctance to hear it from Carter that Ke'ra, as it turned out, was in fact Linea. Fraiser tested the DNA and confirmed it; Ke'ra's DNA was a perfect match to the sample she'd taken from Linea the year before.
According to her last journal entry, Linea discovered a link to longevity to the Dargol, which slowed the aging process somewhat, and attempted to enhance the Dargol's life-extending properties to create a sort of "Fountain of Youth" to reverse her natural old age. She was about to conduct a controlled lab experiment using a highly intensely concentrated form of Dargol on two Vyan elders -- a male and a female. The experiment soon got out of control, as there was some sort of lab accident during the experiment her two lab subjects died, and a Dargol gas cloud was released into the atmosphere, effectively regressing everyone's ages by some 40-50 years and blocking their memories of their former lives.
Daniel fought for Ke'ra's right to live her life because Ke'ra was not the mass murderer that Linea had been. He argued that Ke'ra should not be held responsible for Linea's actions because she did not have Linea's memories nor personality. Once Ke'ra was told that she was Linea, she decided to take the cure for the amnesia which she developed and found that she could not live with the fact that she was something evil, recognizing that even if 'Ke'ra' loved Daniel, 'Linea' would be more than happy to watch him die. Her conflict led to her to attempt suicide, but Daniel stopped her and convinced her to expose herself once again to the chemical which had caused the amnesia. Ke'ra forgot Linea, erasing the Destroyer of Worlds, and everyone else, including Daniel. While in the embarkation room to return to Vyus, she thought that she had known Daniel and asked him if they knew each other well before her memory loss. He said that they didn't and then bade her good-bye. Before walking through the wormhole, Ke'ra turned and smiled at him. (SG1: "Past and Present")