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Past as one of the Final Five
Like the other Final Five Cylons, Foster is a Thirteenth Tribe scientist re-inventing Cylon resurrection technology on Earth. She cohabitates with her lover, Galen Tyrol. When nuclear armageddon comes, she downloads to a resurrection ship the five had placed in orbit, having been warned of Earth's impending doom by messengers invisible to other people.
She and her cohorts travel at relativistic but subluminal speed to warn the other Twelve Tribes (i.e., humanity) about the dangers of creating artificial life in order to avoid another revolt and horrific war. They follow the sign-posts left by the Thirteenth Tribe, such as the Temple of Hopes. Foster and the others arrive during the First Cylon War, too late to have prevented it. They are, however, able to end the war by agreeing to help the Centurions develop humanoid Cylons, a project on which the Centurions had started with little success.
Foster and the other four of the Final Five create eight humanoid Cylon models copied many times over. Number One becomes jealous of the others, particularly Number Seven, and dissatisfied with the body and programming the Final Five gave them. After eliminating the Number Seven line, Number One kills Foster and the other four. He controls their resurrection to repress their memories, and maroons them among the humans, who are unaware of their true nature. (TRS: "No Exit")
Roslin's loyal aide
Prior to the Cylon attack, Foster was precinct captain for the Federalist Party in Delphi for five years, where she became proficient at taking polls (TRS: "The Captain's Hand"). During the Cylon attack, Foster was driving down a road on Caprica talking on her cell phone when the bombs hit. Foster was hit by a nuclear shockwave and while she was injured, her car (which was destroyed) protected her enough for her to survive and she was apparently rescued by a Raptor that landed nearby looking for survivors (TRS: "The Plan"). President Roslin taps her to replace the late Billy Keikeya as Presidential Aide after his demise.
When President Roslin makes the decision to keep the new-born Cylon/human baby as far away from Sharon Agathon and the Cylons as possible, Foster creates a list of hand picked civilians who could be trusted with the baby. In the end, a civilian named Maya is selected to take custody of the child. Foster makes it very clear that the child's mother's identity must remain a secret (TRS: "Downloaded").
Foster later conspires with Saul Tigh and Anastasia Dualla to rig the Presidential election in Roslin's favor. The ruse is uncovered and suppressed by Admiral William Adama and Lieutenant Gaeta (TRS: "Lay Down Your Burdens, Part II"). During the occupation of New Caprica, Foster aides Roslin in compiling a list of humans who are in collusion with the Cylons. Roslin makes her responsible for ensuring the safe transport of Maya and Hera off planet, but she fails at this task. Maya is killed trying to escape New Caprica with the child. Hera survives but is found by the Cylons (TRS: "Occupation", "Exodus, Part I & II").
Before and during the trial of ex-president Gaius Baltar, she is tasked with helping Roslin assemble a tribunal to bring charges against him, as well as establish security arrangements ("The Woman King", "The Son Also Rises", "Crossroads, Part I"). She demonstrates an unwillingness to aid Romo Lampkin's defense case by initially stonewalling Lampkin's attempts to gain access to records on Colonial One (TRS: "The Son Also Rises").
Revelation as a Cylon
Some time after the apparent death of Kara Thrace (TRS: "Maelstrom"), Foster began a sexual relationship with Thrace's widowed husband, Samuel Anders. Roslin apparently learned of the relationship and was displeased (TRS: "Crossroads, Part II"). At the beginning of Baltar's trial, Foster began to show signs of stress, possibly originating from a strange noise which she heard as the Fleet moved towards the Ionian nebula. Her lack of sleep and stress levels resulted in a damaging outburst to the press corps during the press conference at which Roslin discussed the return of her cancer. Roslin confronted Foster after this, threatening to replace her if she did not get back on her game (TRS: "Crossroads, Part I"). When the Fleet reached the nebula, Foster (on Galactica) was drawn to Saul Tigh, Galen Tyrol, and Samuel Anders, who also heard the now-coherent melody. Despite each of them realizing that they are Cylons, Foster and the others re-committed themselves to the Colonial cause. Foster returned to CIC and stood by Roslin, ready to aid (TRS: "Crossroads, Part II").
The four newly revealed Cylons tried to keep their nature hidden from those around them while trying to come to terms with it. When they brainstormed ideas about the still-missing final Cylon, Col. Tigh suggested that Foster flirt with Gaius Baltar to gain access to the knowledge he acquired while living among the Cylons on New Caprica. Although initially repulsed at the idea, she spoke to Baltar and was slightly captivated when he explained how he saw his new role as a religious figure. Although at first she cried when eventually sleeping with him, she was further charmed when Baltar told her that he thought Cylons were people with feelings too (TRS: "Six of One").
Foster also made a pass at Galen Tyrol, who rebuffed her advances but was suspected of having an affair by his wife, Cally Tyrol. After one of their clandestine meetings, Foster noticed an open wall covering, and concluded that they had been overheard by Cally. Not long after that, Foster followed Cally to a Viper launch tube where Cally was about to kill herself and her son Nicholas Tyrol by expelling them out of the tube into space. Foster confronted Cally and explained that they only recently found out they were Cylons, and that they were still the same people, as scared and confused as everyone else. Foster comforted Cally and took Nicky in her arms, then suddenly struck her, throwing her body into the air. She retrieved the launch tube key, exited the launch tube with Nicky in her arms, and used the key to activate the launch controls. As Cally regained consciousness, Foster opened the outer airlock door, sending Cally to her death in open space (TRS: "The Ties That Bind").
Foster showed no guilt over this. She appears to have embraced both being a Cylon and her own version of Baltar's teachings, allowing her to bypass such feelings and adopt an almost hedonistic approach to life. She declared herself to be "perfect," something that disturbed fellow Cylons Saul and Galen, and was in marked contrast to Saul and Caprica-Six's guilty consciences (TRS: "Escape Velocity").
After Downloaded Three was unboxed, now knowing the identities of the Final Five, and brought to Galactica, Foster stayed true her earlier affinity for her Cylon side. Under the pretense of bringing Laura Roslin her medication, she flew to the Cylon basestar, where she was introduced to her fellow Cylons and told Roslin and Baltar about her true nature. During the ensuing stand-off between Three and Galactica over the remaining three Cylons, she helped Three's cause by informing her of Lee Adama's perceived weaknesses (TRS: "Revelations").
When the fleet arrived at Earth and discovered it a barren world rocked by a nuclear catastrophe thousands of years ago and once populated by Cylons, Foster and her fellow Final Five Cylons began remembering details about their past lives on the planet. One detail she clearly remembered was how Anders used to be a musician and used to play a song he wrote for her and their friends, Galen Tyrol and Saul and Ellen Tigh. She and Galen were also lovers at the time (TRS: "No Exit").
After being publicly identified as a member of the Final Five Cylons, Foster took up full-time residence on board the rebel basestar, living with the Twos, Sixes (less Caprica-Six), and Eights (less Sharon Agathon & Sharon Valerii"). Her fellow Cylons appeared to have also given her equal status in their command hierarchy, as evidenced by her conduct during Gaeta's Mutiny. When Laura Roslin was smuggled aboard the basestar, Foster was content to abandon the fleet to its own turmoil and simply jump away to safety, a notion her fellow Cylons supported. Though she repeatedly argued against involving the basestar in the counter-coup efforts, she ultimately conceded to Roslin's plan (TRS: "Blood on the Scales").
During Gaeta's mutiny, Sam Anders was shot in the back of the skull. When he regained consciousness, he remembered his and the others' former life on Earth and after. He retold their story as fast as he could to the other Final Five, including Tory Foster. Like the other Fives, she was a scientist attempting to reinvent resurrection technology. To her and Galen Tyrol's mutual shock, she learned that they once lived together as lovers and were engaged to be married. (TRS: "No Exit") After Anders's apparently unsuccessful surgery (in terms of his regaining consciousness) and his comatose state, Foster urged the other Finals and Caprica-Six to leave for the baseship and leave the fleet to strike out on their own without humanity. Then, Ellen Tigh (the Fifth Final), arrived after a so-called rescue of her from Cavil by Sharon Valerii. Arguments on the merits of staying with the fleet and leaving were exchanged and it came to a vote - Galen and Foster voted to leave, Saul Tigh voted to stay. Although he was presently in a coma, Galen assumes that Anders would had voted to stay based on his emphatic plea to Saul to stay with the fleet. It made the vote a 2-to-2 deadlock with Ellen the deciding vote. At the time, she did not know how she would vote as she was also disturbed by personal revelations of the relationship between the colonel and Caprica-Six. Later, borne of jealousy, resentment and vengeance over Saul having a child with Caprica-Six and the implication that he loved Caprica-Six more than he ever did Ellen, Ellen voted with Foster and Galen to leave humanity, making it a 3-2 result. However, Caprica-Six suffered a miscarriage, brought on possibly by stress caused by an attack in Dogsville earlier and personal confrontations with Ellen over the true love of Saul. Foster, like the others, stayed since Hera Agathon became the only hope of the Cylons. (TRS: "Deadlock")
As the Five recovered over the tragedy of the miscarriage, Foster commiserated with the others including a desperate Galen for the life of Boomer who was about to be transported for trial on the baseship. She agreed with Ellen that they could not interfere with Cylon due process other than being witnesses. Then, she was present when Kara Thrace played the song on the piano in Joe's Bar that switched them on in the nebula. She confronted Thrace as to where she learned that song. Thrace told her it was a song that her father played for her as a child. Later (off screen), she told them that she was playing the music notes written as a drawing by Hera Agathon. By this time, Sharon Valerii had already taken Hera and escaped. (TRS: "Someone to Watch Over Me")
Foster was later present with Saul, as Ellen urged the William and Lee Adama to search for Hera at the Cylon Homeworld. Kara Thrace also stresses that they should search for Hera. Galen, although not revealed in the aired episode, was arrested for his aid in the escape of Valerii and the abduction of Hera, so he was not present. At that meeting, Foster did not render an opinion vocally, but she agreed with Ellen's assertions and helped arrange the Heavy Raider reconnaissance mission after Adama gave his permission. (TRS: "Islanded in a Stream of Stars")
Ellen volunteered the Final Five to go on the mission to rescue Hera, much to Foster's dismay. She was still hesitant when Admiral Adama called for volunteers, but Galen convinced her to come. Foster and her Cylon cohorts remained on Galactica to control Anders, who was plugged into Galatica's systems. (TRS: "Daybreak, Part I")
She remained there for the battle, and was standing next to Anders when Caprica-Six and Gaius Baltar fulfilled the Opera House Prophecy, rescuing Hera and seeing the Final Five standing together. When Cavil invaded Galactica's CIC to take Hera back, Saul volunteered to give him Resurrection technology, which would require the Final Five to share their memories. A visibly nervous Foster knew the other members of the Five would see her killing Cally and tried to get them to forgive her ahead of time, saying they had all made mistakes and they had to move past what they would see. The colonel told her she was forgiven for what she did and she and the other members of the Five connected to the datastream. The shared memories revealed to Galen and the others that it was Foster who killed Cally. An enraged Galen broke the connection and grabbed Foster by the throat, choking her and breaking her neck. With the previous destruction of the Resurrection Hub, her death was permanent (TRS: "Daybreak, Part II").