Biography, courtesy of Wiki (SPOILERS!)
Biography. Agathon, Sharon. [Courtesy of the Battlestar Wiki]

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The biography hidden behind this cut contains some serious spoilers. If you are afraid of spoilers and don't know the story to date, PLEASE, don't click on the cut!

Sharon is a Number Eight model first seen on Caprica shortly after the Fall of the Twelve Colonies and the Cylons decide to use her in an elaborate experiment focused on Karl "Helo" Agathon who is stranded on the planet. She is an identical copy of Helo's friend and colleague Lieutenant Sharon Valerii and the Cylons hope to explore the possibilities of Cylon-human procreation by getting Helo to fall in love with her. Sharon appears to Helo to rescue him after he is captured by a Six and several Cylon Centurions. Unaware that Cylons have developed human models, Helo believes her to be Sharon Valerii from Galactica, returning to rescue him. Following this staged rescue, she leads Helo to a Raptor, now surrounded by Cylon Centurions, and convinces him that they have no direct way off the planet. Sharon is able to impersonate Lieutenant Valerii convincingly, since she has accessed Valerii's entire memories.

After receiving a feigned Colonial signal on a radio receiver they carry, Sharon leads Helo to a city where they find a fully-equipped fallout shelter in which two people can live in reasonable security, hidden from above-ground Cylon operations, and with sufficient supplies to last a considerable period of time. The purpose in establishing this retreat is to elicit an emotional response in Helo towards his Cylon companion. When this fails and Helo continues to seek a way off Caprica, the Cylons lead him to believe that Sharon has been captured, concluding that if Helo does not seek to rescue her, the experiment has failed and he must be killed.

Helo does undertake a successful rescue attempt and shortly after, the two of them have sex for the first time in a nearby forest. Helo had always been fond of the original Valerii on Galactica, but his affection for her was stilled by her relationship with Chief Galen Tyrol. Pleased with the progress, the Cylons set up a new hideout, a cabin in the woods, and Sharon is instructed to lead him there and have him stay with her – or kill him, if he attempts to leave. But she begins to question the Cylons' overall goal. Realizing that she has herself fallen in love with Helo, Sharon disobeys her instructions and leads Helo to Delphi, where they hope to steal a vehicle and get off the planet. On their way to Delphi, she shows signs of being pregnant, succumbing to a bout of morning sickness and developing a ravenous appetite.

More than a year later, and four months after Galactica and Pegasus's retreat from New Caprica, Sharon Agathon is now married to Karl "Helo" Agathon. In the year that has passed, Admiral Adama has taken Sharon into his confidence, granting the Cylon much of the same daughter-figure trust he had given to "Boomer" Valerii and Kara Thrace in the past. Apparently, the two periodically sit down to tea and speak in confidence; her cell now has a couch, a table, and other amenities. Now apparently trusted not only by Admiral Adama but by the crew, Adama commissions Agathon into the Colonial Fleet as a Lieutenant (Junior Grade). In her first mission, Agathon leads an insertion force that will serve as a liaison between the New Caprica Resistance and Galactica during the extraction of the New Caprica population. She commands two Raptors in an intra-atmosphere jump and links up with Samuel Anders and his squad at the Breeders Canyon. Their planning is interrupted when Cylon Centurions ambush their position. Agathon and her assigned Marines anticipated enemy contact, so the Marines, from a supporting position, can neutralize the Cylon attackers.

On the following day, Agathon covertly enters the Cylon detention center to recover the launch keys for the grounded Colonial ships, bypassing human and Centurion guards that cannot distinguish Agathon from other Eights. After interfacing with a data terminal and obtaining the keys, a Number Three enters the room and challenges her loyalty. The Three tells her that Hera is still alive, but Agathon rejects the notion, shoots the Three in each leg to slow her eventual report back to other Cylons. When she hands over the launch keys to Chief Tyrol, she asks him if he had actually seen Hera's ashes, which he affirms.

Following the Battle of New Caprica, the Agathons and many other pilots eat in the mess hall. After Racetrack addresses Agathon as "Boomer", Helo asks the crew for suggestions for a more appropriate callsign. A number of humorous and affectionate responses arise (reflecting Agathon's trust and comfort amongst the human crew), but Helo opts for Hot Dog's suggestion, "Athena".

Agathon undertakes a solo recon mission through a high radiation cluster to look for a planet with suitable material to replenish the Fleet's lost food supplies. Agathon's Cylon physiology withstands radiation levels that would have killed a human, although not without some discomfort. The successful mission confirms the foodstuffs on a planet with algae and gives needed data to safely attempt the guide the Fleet.

During a stand-off at the Algae planet, a Cylon delegation boards Galactica to negotiate for the Eye of Jupiter. Agathon, near the conference area, instantly identifies the Eight from the baseship delegation as the consciousness of the former "Boomer" Valerii. Boomer-Eight tells Agathon that her daughter is still alive and also notes President Roslin's involvement in her daughter's disappearance. After confirming the matter with Roslin, Admiral Adama confirms to the Agathons that Hera's death was indeed fabricated without his knowledge. Agathon says, with more than a hint of anger and matter-of-fact tone, "I want to see her."