Number Eight (Sharon "Boomer" Valerii / Sharon "Athena" Agathon)
Sharon "Boomer" Valerii first appears as a Raptor pilot aboard the Galactica. Her true nature as a Cylon was only revealed at the end of the miniseries, and the series quickly establishes that Sharon acted as a sleeper agent, unaware of her true nature and programmed to carry out attacks on the fleet without her human side realizing what she was doing. She was revealed to be the eighth model in "Downloaded".

Also interesting enough, at the end of the mini series, a number Six says "By your command" to an Eight. This phrase is usually spoken to the Imperious leader in the old series by Centurions. It seemed to give this particular Eight a leadership role.

The other significant copy of this model, Sharon "Athena" Agathon, married Karl "Helo" Agathon, rebelled against the Cylons and joined forces with the Colonials. Her child with Helo, a daughter named Hera, is the first Cylon/human hybrid to be born. Such a child is the subject of a Cylon prophecy and therefore very important as it was a 'child born of love'. Shortly after Hera's birth, Laura Roslin decides to mislead the Cylons into believing the child has died. Her plan involves lying to Athena and Helo, and giving the child to an adoptive mother, Maya. While aiding the Colonials in their plan to rescue the humans on New Caprica, Athena sneaks into a Cylon storage facility and steals launch codes for the civilian ships trapped on New Caprica by the Cylons. During this action, Athena is discovered by D'Anna Biers. D'Anna informs Athena that Hera is still alive, citing strange dreams and a prophecy by a human mystic as proof. Athena, believing this to be a ruse, kneecaps D'Anna. During the exodus from New Caprica, Maya is killed and the baby is found by D'Anna. Athena is later told, by Boomer, that Hera lives. Athena has Helo kill her, allowing her to download into a new body within the Cylon fleet. With the help of Caprica Six, she manages to rescue Hera and return to Galactica.

This model has been described as "weak" by Baltar's vision of Number Six, and Number Eights usually appear more compassionate and sympathetic than other Cylons. However, they fully supported the destruction of the Twelve Colonies; and the actions in particular of Boomer and an Eight who had a duplicitous affair with Felix Gaeta on New Caprica make it clear that Eights are capable of homicide and betrayal. Eights are also capable of intense loyalty and have the ability to break from Cylon traditions and laws to help human friends or family. They also voted to save humanity in the Cylon civil war started by Sharon (Boomer). She hesitated for a while when Cavil started to influence her, but in the end she chose to support the humans, even if it meant that she would have to give up her life. Sharon (Athena) became completely assimilated in human culture. Her child and husband became her focus in life. She seemed to be the only Cylon to accomplish a normal family existence. The model Eight's perceived fragility seems to camouflage great strength and direction. (In one episode, Sharon (Athena) was able to "hard" wire herself to the Galactica, hack into a Cylon fleet and shut them all down.) Eights seem to enjoy being with humans for the most part.

Number Eights are played by Grace Park.