Number One (John Cavil)

Ones subvert consensus by undertaking many actions without the knowledge or consent of their siblings, such as turning against the Sevens and the Final Five, and then reprogramming their siblings to hide this.

John Cavil initially poses as a priest.^[3] His true identity is revealed when a second copy boards Galactica and reveals his Cylon nature. Cavil's role in society is contradictory. He occasionally serves as a devil's advocate, pointing out the absurdity of his fellow Cylons and their religious zealotry.^[4]

Cavil has a sadistic, Machiavellian streak that none of the other Cylon models share. He tortured Saul Tigh by gouging out one of his eyes and showing it to him. He took pleasure in blackmailing Ellen Tigh into providing sexual favours in exchange for releasing Saul from captivity on New Caprica.^[5]

Cavil is an atheist (alone among the seven models), and often mockingly uses air quotes when saying the word "God". His opinions of humans are contradictory. He is one of the most violently anti-human Cylon models, advocating a policy of culling humanity down to a "controllable number".^[5] He claimed to have been against the destruction of the Twelve Colonies and advocates a unique Cylon Society, not one that emulates its creators. After arranging Tigh's release, Cavil further manipulated the situation by again blackmailing Ellen to betray the human resistance on New Caprica and threatening to kill Saul if she did not comply.

Cavil is aloof compared to the other models, though Boomer implies that Cavil has begun teaching her his views that Cylons should not emulate humanity. Cavil knows aspects of Cylon lore that the others models do not. His knowledge of the Final Five led him to box the D'Anna and the other Threes to ensure that whatever she had learned about the Final Five stayed hidden.

He was made in Ellen's father's image. Ellen also named him "John". He hates this name and shows deep resentment towards Ellen at being "limited" by having to live in a humanoid body.

One was the first model and helped the Final Five create the other seven. Therefore, Ones knew the identities of the Final Five while the others knew only that they existed. For an unstated reason, Cavil rejected the human trait of mercy and turned against the Final Five.

When the Final Five were resurrected, Cavil implants new memories for their life in the Twelve Colonies. He also alters the original programming of the seven other models so that searching for, talking about, and even thinking about the Final Five was strictly forbidden.

Ones are played by Dean Stockwell.

Number Two (Leoben Conoy)

Leoben first appears as a smuggler at the munitions depot at Ragnar Anchorage, where he was exposed as a Cylon.^[6] Twos are religious zealots, carrying a pathological, and sometimes sexual, obsession with Starbuck. His Cylon identity was revealed ("Six of One").

Twos are skilled at deceit. Conoy manipulates Starbuck into thinking that a young girl he had kidnapped on New Caprica is her biological daughter. Twos display cunning minds and the ability to find and exploit others' weaknesses. Unlike other Cylons, Twos appear to be prescient and on several occasions prophesy future events.

Twos are played by Callum Keith Rennie.

Number Three (D'Anna Biers)

D'Anna Biers was a reporter for the Fleet News Service. Roslin and Adama grant Biers access to all areas of Galactica to investigate her suspicions of a military cover-up surrounding civilian deaths aboard the Gideon. Their belief is that Biers will discover that military personnel deal with the same pressures and fears as the rest of the fleet, and that the events were a tragic mistake. The Biers model used the documentary as a means to relay information that Sharon was alive to Cylons on Caprica ("Final Cut"). D'Anna was revealed to be a Three in the episode "Downloaded".

Threes are among the more aggressive models, and share a fatalistic understanding of the Cylon religion, believing that everything that happens is the will of God. Their religious devotion masks a deep questioning by Threes about why God allows bad things to happen (Theodicy).

Threes possess aggressiveness, advancing themselves as de facto leaders in any situation. They are often rivals of Ones and Sixes. The rivalry with the Sixes partly stems from when Caprica-Six killed a Three to save Sam Anders from torture and death. D'Anna and Caprica-Six later reconcile and both of them are involved in a relationship with Baltar. Baltar seduces D'Anna by exploring her crisis of faith, which leads to her secretly committing suicide (a major Cylon taboo) to experience resurrection. She feels these near-death experiences will answer questions regarding her faith, notably the identity of the Final Five. D'Anna eventually sees the faces of the Final Five ("Rapture"). Unfortunately, as she does so, the other Cylons vote to box all Threes. Cavil tells her that what she had seen regarding the Final Five was unacceptable and that her memories would be kept in "cold storage". D'Anna, but not the other Threes, is later unboxed ("The Hub").

Threes are among the more anti-human Cylons. D'Anna tells Baltar that she believes that humanity must die to prevent future generations of humans from seeking revenge ("Exodus" Part II). She is temporarily the leader of the "rebel" faction of Cylons that makes peace with the human fleet, but when the first Earth is found to be a devastated ruin, she decides to stay there and die rather than continuing the cycle of death, exodus and rebirth.

Threes are played by Lucy Lawless.

Number Four (Simon O'Neill)

O'Neill poses as a human physician who treats Starbuck for a gunshot wound in what was supposedly a resistance hospital on Caprica ("The Farm"). In reality this was a Cylon "farm" set up to breed human-Cylon hybrids using captured humans. Simon performed invasive tests on Starbuck's reproductive organs. He was revealed to be the 4th model in the episode "Six of One". Fours are consistently medical specialists.

Another Four poses as a married man in the Colonial Fleet. Cavil at one point asks Simon to leave his life behind and destroy the ship he lives on. He defies this order to protect his wife and her child by committing suicide and flying out of an air lock. He was not close enough to a Resurrection Ship and therefore died permanently ("The Plan").

Fours are played by Rick Worthy.

Number Five (Aaron Doral)

Doral debuts as a public relations worker for the abortive Galactica museum (miniseries). Another Five sneaks aboard the Galactica and detonates an explosive ("Litmus"). This event prompts the fleet-wide announcement that Cylons can have a human appearance. He was revealed to be the 5th model in the episode "Downloaded."

During the Occupation of New Caprica, the Fives are anti-human and aggressive. They specialize in public relations and control, using large-scale events and media manipulation.

Fives are played by Matthew Bennett.

Number Six (Caprica-Six / Shelly Godfrey / Gina Inviere / Natalie Faust / Lida / Sonja)

The first model explicitly revealed to be a Cylon in the mini-series, Sixes often use seduction to their advantage. Important copies include Shelly Godfrey, Gina Inviere, Head Six, Caprica Six and Natalie.

Caprica Six

The first Cylon seen, Caprica Six had a two-year relationship with Baltar on Caprica, during which she used him to gain access and plant the backdoors in Colonial military network software which enable the total success of the initial Cylon attack. She sacrifices her body to save Baltar's life from a blast wave of that Cylon attack. She then exists for the rest of the series in Baltar's imagination as his "Inner Six," in addition to returning in corporeal form which is then known by the nickname "Caprica Six."

Caprica Six has a love-hate relationship with Baltar, alternately defending him to other Cylon models or leaving him to suffer at their hands.

A reincarnation of Caprica Six commits the first incident of Cylon-on-Cylon violence, killing a Three with a rock to save Anders's life.

Caprica Six was imprisoned on Galactica after helping Athena escape from the Cylons with Hera. She offers to testify against Baltar. While in the brig, she has a relationship with Saul Tigh. This results in the first Cylon-Cylon pregnancy in 2,000 years, which ends in a miscarriage.

Caprica Six has an "Inner Baltar" which only she sees, similar to how Baltar has an "Inner Six" that only he can see; Inner Baltar serves as a sort of conscience for Caprica Six and as an advisor in times of trouble, as Inner Six does for him. Inner Baltar appears at least once to Baltar himself. Before their true nature is revealed, speculation rises that Baltar is a Cylon. Inner Baltar and Inner Six appear to Baltar and Caprica Six – all four sharing a moment together – as the first part of the revelation that the "Inners" are divine beings (referred to as "Angels") manipulating both the Colonials and Cylons into fulfilling "God's plan" (series finale).

Shelly Godfrey

Godfrey was on Galactica after the Cylon attack. She accused Baltar of treasonously sabotaging human defenses, and therefore of killing several million people (Six Degrees of Separation). She also appears in Battlestar Galactica: The Plan TV movie.

Gina Inviere

Gina acted as a contractor for Pegasus and was in a relationship with Admiral Cain. When Cain discovered that Gina was a Cylon agent, she ordered her crew to "push her programming" in an attempt to see if Gina was vulnerable to emotional trauma. Gina later escaped with Baltar's aid, assassinated Cain and founded a resistance group in the fleet, preaching peace with the Cylons. While it seemed that Gina developed feelings for Baltar and wanted to pursue him, she detonated a nuclear warhead (provided by Baltar) that destroyed Cloud Nine, other fleet ships and generated an electromagnetic signature, the detection of which ultimately led the Cylon fleet to New Caprica.

Sonja and Natalie

Other important Sixes include Natalie, who originally leads the rebel Cylon faction against Cavil's faction before she is killed by Athena in a misunderstanding, and Sonja, who was elected to represent the rebel Cylons in the Colonial fleet's Quorum of Ships' Captains.

Sixes are played by Tricia Helfer.

Number Seven (Daniel)

Daniel was the seventh Cylon model ("No Exit"). Ellen refers to Daniel as an "artist, and so sensitive to the world". She was very close to Daniel, which enraged Cavil; he felt that Daniel was Ellen's favorite and became jealous. Cavil poisoned the amniotic fluid used to mature the Daniel copies and then corrupted Daniel's genetic code. This sabotage meant that no further Sevens could be created. The original was also killed with Sam Anders stating at one point that "Daniel died" after regaining his true memories.

Fans speculated that Starbuck or her father was a version of the corrupted Seven line. Instead Daniel is merely a plot device to explain the missing number and to expand on Cavil's character (noting that Daniel is essentially the Abel to Cavil's Cain).^[7] The Sevens were a springboard for Caprica, where Daniel Graystone is the name of a main character played by Eric Stoltz; this Daniel is the creator of the Colonial Centurions.^[8]

Sevens are never seen in the series, and their physical appearance is never described.

Number Eight (Sharon "Boomer" Valerii / Sharon "Athena" Agathon)

At the end of the miniseries, a 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. Eights also appear to be designed to be extremely beautiful, to seduce as a sleeper agent. But Eights have been noted to actually fall in love by personal choice with humans. This theme has been seen throughout the series and DVD movies produced after.

Boomer

Sharon "Boomer" Valerii first appears as a Raptor pilot aboard the Galactica. Her true nature as a Cylon was revealed at the end of the miniseries. She acted as a sleeper agent, unaware of her true nature and programmed to carry out attacks on the fleet without realizing what she is doing. She was revealed to be an Eight in the episode "Downloaded".

Athena

The other significant Eight, 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. Such a child is the subject of a Cylon prophecy. Its importance increased as it was a "child born of love". Shortly after Hera's birth, 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. She is discovered by D'Anna, who informs her 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, Hera's caregiver is killed and D'Anna finds the baby. Boomer later tells Athena that Hera lives. Athena has Helo kill her (Athena), allowing her to download into a new body within the Cylon fleet. With the help of Caprica Six, she rescues Hera and returns to Galactica.

Eight is described as "weak" by Baltar's Head Six, and Eights usually appear more compassionate and sympathetic than other Cylons. However, they fully supported the destruction of the Colonies. The actions 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 vote to save humanity in the Cylon civil war that Boomer starts. She hesitates for a while when Cavil influences her, but in the end chooses to support the humans, even if it means that she must give up her life.

Athena becomes completely assimilated in human culture. Her child and husband become her life's focus. She is the only Cylon to create a family. The Eights' perceived fragility camouflage great strength and direction. In one episode, Athena hardwires herself to Galactica, hacks into a Cylon fleet and shuts them down.

Eights are played by Grace Park.