From Battlestar Wiki, the free, open content Battlestar Galactica encyclopedia and episode guide
Her consciousness is downloaded and she is reborn in another body. Subsequently, she experiences severe problems integrating into Cylon society and long considers herself more human than Cylon. She eventually works together with Caprica-Six in an attempt to change Cylon popular opinion about humans and she emerges as one of the Cylon leaders jointly responsible for the end of the occupation of the Twelve Colonies and later the Cylon occupation on New Caprica. Following the failure on New Caprica, Valerii abandons her hopes for coexistence with humans and she denounces her past on Galactica. She is assigned to watch Hera Agathon, but when Hera's mother comes to rescue her, Boomer tries to kill her and is killed by Caprica Six allowing Agathon and Caprica Six to escape while Boomer downloads to a new body again. However, while she feels that she belongs to Cylon society, she is not fully integrated into it and relatively isolated among her peers, particularly from the rest of her model's line as her vote to lobotomize the Cylon Raiders leads to a Cylon Civil War.
She is engaged in a relationship with the Number One leading the pro-lobotomization faction of the Cylons and is a member of that faction although she does express some misgivings about their actions. She is also aware of the identity of at least one member of the Final Five: Ellen Tigh and has known since before even D'Anna found out as Cavil trusts her and let her in on the secret.
Later when she is prisoner on Galactica she escapes, beats Athena badly, has sexual relations with Helo and kidnaps Hera, but redeems herself somewhat by saving Hera from dissection and helping her escape to her parents. Boomer is finally killed by Athena and with resurrection destroyed, her death is final.
Life on Galactica
Valerii is a "sleeper" agent, unsuspecting of her Cylon status. As far as she is aware, she was born on the mining colony of Troy, as the daughter of a family from Aerilon (Flesh and Bone). Troy itself was destroyed in an unexplained cataclysm, allowing Valerii's background to be established as that of an orphan. Following her arrival on board Galactica, she enters into a relationship with the ship's Chief Petty Officer Galen Tyrol, which is against military protocols concerning fraternization between officers and non-officers. Whether this is unintentional or a subconscious reaction to her Cylon programming remains unclear.
As a rookie pilot, she keeps missing the trap and putting holes into the deck. Admiral Adama calls her to his office alongside Colonel Tigh and talks with her about why she keeps doing that and instead of kicking her out of the service, he gives her advice and another chance. Boomer thanks him and tells him she owes him one and will pay him back someday. Adama says a lot of people owe him one but a lot never pay it back but Boomer promises to pay him back someday when it really means something.
At the time of the Cylon attack, Valerii is flying her Raptor to Caprica with Galactica's last remaining operational Viper squadron, when they learn of the attacks and attempt to engage two Cylon Raiders. However, the Viper squadron is destroyed, and the Raptor is damaged while trying to escape, forcing Valerii and her ECO Karl Agathon to make an emergency landing on Caprica in Raptor 312.
After repairing the Raptor they are mobbed by desperate civilians and undertake a rescue operation. Lifting a number of children, Valerii states there is room for three adults. Valerii holds a lottery for the three seats. When the last number is called, Agathon chooses to give up his place aboard the Raptor so that Doctor Gaius Baltar can be rescued as well (Miniseries). Helo later manages to make it back to Galactica with the help of Starbuck and another Sharon months later.
After being found by Laura Roslin's group of stranded military and civilian ships, Valerii works within the new civilian Fleet, assisting Roslin's attempts to gather other stranded civilian ships in the space surrounding Caprica. She finds a number of ships critical to the fledgling Fleet's survival, such as a fuel tanker. After the newly assembled Fleet, led by Galactica, leaves the solar system of the Colonies, Valerii aids in other critical acts, including the discovery of a tylium-rich asteroid, replete with an active Cylon mine (The Hand of God), and locating a source of water to replenish the Fleet's lost supply after the sabotage of Galactica's stores (Water).
Acts of sabotage
At the same time as she is supporting the human Fleet, Valerii's underlying Cylon subroutines periodically emerge. Her Cylon programming is the cause of the sabotage of Galactica's water tanks (Water). Later, she likely assists a copy of Aaron Doral to access a munitions store. The Doral copy constructs a suicide bomb which nearly kills Commander Adama and Colonel Tigh (Litmus).
Valerii finds herself soaking wet, after she awakes to her human personality shortly after the bombs used to destroy Galactica's water tanks were planted. She becomes increasingly concerned and starts to question her true self. Her worry increases when she experiences a certain attachment to a captured Cylon Raider, and is able to give insight into how it can be properly assessed and understood ("Water", "Six Degrees of Separation", "Flesh and Bone"). Her concerns are further elevated when, following the bombing by Doral, Galactica's Master-at-Arms, Sergeant Hadrian, suspects her and Chief Galen Tyrol of Cylon complicity (Litmus).
Tyrol distances himself from Valerii after this incident, and he later ends their relationship following the arrest of Specialist Socinus (Litmus). Facing Tyrol's suspicions concerning her activities immediately before the bombing, Valerii finds herself emotionally isolated and stressed. She takes the Cylon detector test created by Dr. Baltar, but he hides her positive test result in fear that once discovered, she might immediately retaliate and kill him (Flesh and Bone). Valerii finds short solace in Baltar's test, but deals with an anonymous accusation, when she finds the word "Cylon" written on the mirror of her locker; though it is possible she wrote it herself, unknowingly (Six Degrees of Separation).
Frightened and alone, Valerii withdraws into herself and attempts suicide, but is initially unable to do so. During her second attempt, she is interrupted by Dr. Baltar who, rather than discouraging her, essentially gives her his blessing on her suicide. Following his departure from the duty locker, Valerii succeeds in shooting herself, but her Cylon personality interrupts the attempt. Valerii only wounds herself in her right cheek (Kobol's Last Gleaming, Part I).
After Kara Thrace absconds with a captured Cylon Raider intended for an attack on a basestar orbiting Kobol, Commander Adama asks Valerii and ECO Margaret Edmondson to use a Cylon transponder in their Raptor to infiltrate the basestar and place a nuclear warhead within to destroy it. The mission is a success, but when the weapon would not auto-release from the Raptor after landing, Valerii exits the ship and enters the basestar. Inside, she encounters a dozen copies of herself, confirming her worst fears. Valerii escapes in the Raptor just before the warhead detonates and destroys the basestar. Back on Galactica, her encounter with the other Eight models on the basestar apparently triggers Valerii's Cylon programming to emerge once more, and she shoots Commander Adama in the chest while being congratulated on her successful mission in CIC, wounding him critically ("Kobol's Last Gleaming, Part II", "Scattered").
Imprisonment and death
After shooting Adama, Valerii is quickly restrained by guards and jailed in the brig. During her imprisonment, Colonel Tigh attempts to forcibly extract information from her at gunpoint, but Valerii stonewalls him and even asks him to shoot her (Scattered). Chief Tyrol is later incarcerated in the same brig cell by Tigh, also suspected of being a Cylon. While imprisoned together, Valerii tries to convince Tyrol that her feelings for him were real and important, but he rejects her and threatens to kill her if she touched him.
Dr. Baltar later enters the cell, ostensibly to collect a blood sample from Tyrol to prove his innocence using the Cylon detector, but he instead injects Tyrol with a potent toxin that would kill him in a matter of seconds if Baltar does not give him an antidote. Baltar interrogates Valerii, demanding to know how many other Cylons are in the Fleet, using the dying Tyrol to blackmail her. Valerii first protests that she does not know, but as Tyrol is about to die, she reveals that there are eight other Cylons in the Fleet and Baltar then revives Tyrol.
Soon after, while being transferred to a new reinforced cell built to hold Cylons for later experiments and long term incarceration, a large crowd of crewmembers jeers at her and calls her a traitor. Specialist Cally who considers Valerii responsible for Tyrol's imprisonment breaks through the crowd holding a gun and shoots Valerii at point-blank range. Valerii's last words are "I love you, Chief" and she dies in Tyrol's arms (Resistance).
Valerii's body is sent to the morgue and autopsied. Later, the recovered Commander Adama visits her corpse, asking "why" aloud, and weeps over her body. Adama pronounces a very mild reprimand for Cally, sentencing her to 30 days in the brig for discharging a weapon without authorization. Cally is never tried for murder, since Cylons are not seen as people (The Farm).
Valerii's corpse is later used as bait when Sesha Abinell takes over Cloud 9, demanding the execution of the future Sharon Agathon. The distraction provided a window with which to diffuse the terrorist situation. (Sacrifice)
Rebirth and life among Cylons
After being shot by Cally Henderson, Galactica is close enough to a Cylon Resurrection Ship so that her consciousness is retrieved for download into another body. On rebirth, Valerii rejects her Cylon nature and continues to call herself "Sharon" instead of "Eight," even going so far as to reclaim her former apartment (502) on Caprica. A copy of Number Three, representing the status quo of the Cylons, is deeply disturbed by this and suggests that Valerii be boxed.
Caprica-Six, also seen as a Hero of the Cylon, protests and Three advises her to get Valerii to change. When Valerii laments the loss of Tyrol, Caprica-Six tells her about her own love for a human, Baltar, which prompts Valerii to inform her that he is still alive. Suspecting that Three has an ulterior motive and wants to box both of them, the two play along and Valerii announces her intent to move out of her old apartment. After a Caprica Resistance bombing, Valerii, Caprica-Six, and Three are trapped in a garage with the resistance's leader, Samuel Anders. There, Caprica-Six reveals their true intentions and declares that Valerii and herself are celebrities in a culture of unity, and, through their love for humans, have realized the horror of the Cylons' actions. Using their celebrity, they could convince a large portion of the Cylon society of their new belief that the genocide of humanity was wrong. Valerii stops Anders from killing Three, but is surprised to see Caprica-Six kill Three herself. After telling Anders to escape, Valerii agrees to help Caprica-Six reveal the truth of the genocide to the other Cylons (Downloaded).
Valerii and Caprica-Six are obviously successful in their attempt to change popular opinion among Cylons about the genocide on the human race. According to a Cavil model that is briefly incarcerated on board Galactica, Valerii and Caprica-Six convinced a majority that "the slaughter of mankind was a mistake" which ultimately leads to an end of the occupation of the Twelve Colonies (Lay Down Your Burdens, Part I).
One year later, Valerii is one of the leaders of the Cylon force occupying New Caprica. But as other Cylons start to consider the occupation a failure, her influence appears to decrease quickly, most evident when she is unable to secure Henderson's release from detention or to remove her from the death list (Precipice). Their initial plan on New Caprica, "to push past the conflict that separated us from humans for so long", fails and the occupation is ended after four months (Exodus, Part II).
Following the retreat from New Caprica, Valerii is on the same basestar as Caprica-Six and Baltar, and assigned responsibility for the Cylon-human hybrid child, Hera Agathon. At a stand-off with the human Fleet at the algae planet, Valerii is part of a Cylon delegation to make demands regarding the Eye of Jupiter, but on board Galactica, she is identified by Sharon Agathon and denied entry. During this first meeting between them, Valerii informs Agathon that her daughter, Hera, is still alive, and she suggests that Agathon will never be fully accepted among humans, because they continue to treat her as a thing (The Eye of Jupiter).
After Agathon downloads into the Cylon fleet to recover her child, it becomes clear that Valerii resents her, possibly out of jealousy for her connection with Hera and Agathon essentially replacing her on Galactica. Valerii has been growing increasingly frustrated by her inability to make progress with the child. She also states that she is done with her past on Galactica and that the failure of New Caprica has taught her that humans and Cylons cannot coexist. When Agathon insists that Hera is suffering from a blocked intestine after she determined that her stomach was "as hard as a gourd" and must be brought to a human doctor who knows how to care for an infant, Valerii immediately suspects that it was the other's intention all along to take Hera back to Galactica, although she is forced to admit that the child's belly has become "hard as a gourd". Suggesting that Cylons were never meant to have children in the first place, Valerii threatens to kill Hera but is knocked to the floor by Caprica-Six and killed by her former comrade (Rapture).
After the Cylon Raiders refuse to take any offensive action for fear of harming the Final Five Cylons in the human fleet, Valerii votes in favor of lobotomizing them into effective fighters once again. This is in contradiction to the opinion of the rest of her model, breaking the stalemate between the Ones, Fours, and Fives in favor of lobotomization and the Twos, Sixes, and Eights against it. Valerii's explanation is that, "we need to be able to defend ourselves." Natalie accuses the Number One that she calls "Cavil" of having influenced Valerii (Six of One). The two are romantically engaged, as they kiss shortly after Cavil's resurrection, and later questions Cavil's decision to attack Natalie's rebel faction at the onset of the Cylon Civil War (The Ties That Bind).
"Escape" from John Cavil
After Ellen Tigh's resurrection, John Cavil allows Boomer to witness his numerous conversations with Ellen. Initially agreeing with John's disdainful view of Ellen, she eventually establishes a bond with her and comes to sympathize with Ellen's perspective on Cylon creation. When Cavil has the Simons prepare to surgically dissect Ellen's brain to extract her memories, she escapes with Ellen in a Raptor logged as missing by the Colonials over a year ago. The two somehow find the Fleet, and after Boomer's voice is identified as an Eight by a Six flying CAP, the Raptor is allowed to land on Galactica. No one realizes who she is until Tyrol approaches, senses who she is, and announces her identity, eliciting a smile from her when he tells her it's nice to see her. Upon hearing this, Admiral Adama has her taken to the brig. Unknown to them at the time, Boomer's "escape" was engineered.
Escape from Galactica
The Cylon rebels decide to put her on trial for treason and, with death permanent because of the loss of resurrection, capital punishment is possible. When Tyrol goes to see her in the brig, she confesses that she still loves him and has thought of him ever since she died in his arms. She shares with him projections of their dream home on Picon, which she has been harboring for a while. In this dream life, they are married and have a daughter. Sure that she is going to be found guilty and executed, Tyrol helps her escape by switching her with another Eight he assaulted and rendered unconscious and placed in Boomer's cell. Boomer then severely beats Sharon Agathon and hides her, bound and gagged, in a toilet stall. She is then mistaken by Karl Agathon for his wife and is sexually pursued by him after she tried to quietly and discreetly without tipping him off to her true identity avoid his advances and to ostensibly leave on her (i.e Athena's) mission. Eventually she acquiesces and even gladly has sex with Karl Agathon without his knowledge as to who she truly was. During the encounter, and most likely without Boomer's knowledge, her victim Athena had become semi-conscious and witnesses Boomer's encounter with her husband from the toilet stall. Boomer then kidnapped the Agathon's daughter, Hera, drugging her with a drink when she picks her up at the daycare center to keep her quiet.
Boomer hides the drugged Hera in a provisions supply case, which is loaded onto a Raptor with Tyrol's help without attracting much attention as such cases have become routine for extended search patrols. Before Tyrol leaves, after he turned down her plea for him to come with her, she tells him that no matter what happens, she wasn't lying about everything she has told him and that she meant it with all her heart, leading to Tyrol kissing her. While waiting for clearance to depart, she figures out that she has been discovered, and against Admiral Adama's orders powers up the Raptor and spins up its FTL drive. She hurriedly flies the Raptor out of the closing flight pod, clipping her port wing, then jumps away, close enough to damage Galactica from the resulting spatial disruption.
While talking with Saul Tigh Ellen later concludes, correctly, that everything that Boomer did, including helping her escape, was planned in order to kidnap Hera and bring her to John Cavil.
Boomer keeps jumping her stolen Raptor, heading for The Colony. Hera repeatably cries for her mother, irritating Boomer. Boomer goes to sedate her with a large hypodermic needle roughly but can't bring herself to do it. Instead she tells Hera about her projection of her and Tyrol's home on Picon and Hera surprises her by revealing she can project too and joining her in the projection. Boomer shows Hera the bedroom she dreamed of for her daughter and bonds with the girl. She ultimately takes her to Cavil but starts crying bitterly when Hera calls out for her showing she regrets her actions. Later when Boomer, Simon, Cavil and Doral are sitting and watching Hera draw, Cavil reveals that Hera has apparently refused to eat and wants to intubate her. Boomer, the only one who seems to have any sympathy at all for the child, objects saying Hera wants her mother, but Cavil doesn't care only wanting to find the secret in Hera's genetic code that allowed her to come into being so the Cylon race can survive. He leaves and Boomer watches unhappily as Simon starts up a drill and prepares to intubate Hera to force her to eat.
Final Act and Death
During the Battle of The Colony, Boomer is with Hera and the Simon who still plans on dissecting her despite the invasion force, confident that the humans will lose. Boomer snaps his neck, killing him and takes Hera and carries her away. She carries her to the rescue team which is searching for her and gives Hera back to her parents. Athena points out that it doesn't make up for what she did and Boomer admits that she knows that, but she made what she knows will probably be her final choice and saved Hera. She tells them to tell Admiral Adama she owed him one (for him giving her another chance rather than kicking her out of the service which she promised to pay him back for) and that their Raptors have been destroyed so they can't get out that way. When Athena points a gun at her, Boomer just stands there and doesn't try to get away. Athena shoots Boomer, killing her and with resurrection destroyed, Boomer's death is final.
The Psychological Damage and Choices Made
"Did Boomer really love the Chief? That’s an interesting question and one I don’t have a neat answer to. Boomer is deeply conflicted. I think the process of having false memories planted in her, getting switched “on” as a Cylon, shooting Adama, getting shot by Cally, and her experiences on New Caprica have left her severely disturbed. She was determined to go through with her mission, but in the process of seducing Tyrol she reawakened feelings of love that she thought were dead. I think she experienced real misgivings just before she got on that Raptor, but felt she had gone too far to back down. Wrapped up in that is her perverse envy of Athena, who obtained everything Boomer once wanted, and this festered into a sick desire to strike out at Athena. It’s difficult to say someone who did that loves the Chief, and yet in her damaged way, I think she did and still does love him." ----David Weddle
"Boomer is much more tragic and conflicted, and in a lot of denial. Athena came from a very different starting point, and everything was a lie, but she fought and made it through the trenches. She's a story not of privilege, but about creating whoever you want to be. That's the American story. Boomer could have been a number of things too, but she made a lot of poor decisions." ---Grace Park