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- Note: This article is protected from edits and kept around as an archive of the speculation that took place before the reveal of the final Cylon. See also Humanoid Cylon Speculation for another such page.
A central mystery of the fourth season concerns who the last member of the Cylon Final Five is. What follows is a compilation of significant clues suggesting or refuting that a character is the final Cylon.
Notes on Clues
Clues as to the identity of hidden Cylons have been historically rare in the series. These are the clues which have actually pointed to a real Cylon:
Clues entered here must be concrete, from canon or official sources. They should be either:
- Extrahuman events relating to a character.
- Clear dramatic references to a Cylon nature.
- Statements from official sources.
Simple suspicious activity or hidden motives are found in all characters and should not be included. Clues should relate to specific extrahuman/Cylon events, or specific foreshadowing, not speculation of what might be true.
Any character, with the likely exceptions of Karl Agathon and Cally Tyrol, who have fathered half-Cylon children with Cylons, could be the final Cylon. The Final Five are a "fundamentally different"
kind of Cylon  and having children, apparent parents, a deep history including experience in the first Cylon war, injuries and a green light from the Cylon detector do not disqualify a character. Connection with the Temple of Five and Earth suggests the final Cylon is, in some sense, older than the colonies. Dead characters are not excluded. The final Cylon may or may not be aware of his or her nature. It is expected that the unmasking of the final Cylon will be a highly dramatic event, similar in grandeur to the revelation of the other four members of the Final Five.
The agenda of the Final Cylon and Final Five is unknown, but appears to not be directly aligned with that of the Significant Seven. The Final Five, or somebody acting for them, acted in the early programming of the Significant Seven to install a compulsion not to think of the Final Five. D'Anna Biers's vision of the Final Five led her to speak of "the one who programmed us." (Rapture)
The 11 revealed Cylons are 7 males and 4 females. A female final Cylon would lessen, but not fully correct that imbalance.
Statement by the First Hybrid
The First Hybrid says this about the final Cylon:
- "The fifth is still is in shadow, drawn toward the light, hungering for redemption, that will only come in the howl of terrible suffering." (Razor)
Four with the Fleet
D'Anna Biers states that "Four [of the Final Five] are in your fleet." (Revelations) At the time, Gaius Baltar, Laura Roslin, William Adama and Karl Agathon are not with the Fleet. Furthermore, Diana Seelix and Brendan Constanza, as well as several minor characters are away from the Fleet too. However, it is uncertain if she intends the statement to be so accurate as to exclude everyone who is not literally with the Fleet at that time, although she only demands four be delivered and is prepared to destroy the Fleet with nuclear weapons, which would destroy the fifth if he/she is hidden within the Fleet.
- Just before being boxed, D'Anna Biers tells Cavil, "There are five other Cylons, brother," ruling out any of the seven known models as also belonging to the Final Five (Rapture).
- The often prophetic Leoben Conoy tells Laura Roslin that "Adama is a Cylon." At that time he should have no knowledge of the Final Five, and programming not to think about them (Flesh and Bone).
- Gaeta's song about a female sleeping being in the shirt of man, whom he prays will awake may suggest a female final Cylon sleeper.
- Season 4 will "further blur the line between Cylon and human" and "redefine what it is to be a Cylon"
- Bradley Thompson stated "If memory serves, [the identity of the] fifth (which may change) we've been kicking around since about the end of Season One."
- During a Q&A session on the official Sci Fi channel Battlestar Galactica forum Ronald D. Moore notes that he already knows who the last Cylon is, and that he's already left clues as to who it is.
- The fifth Cylon will be "organic and satisfying. It won't be some day player from Season 1." says SciFi Channel VP Mark Stern. Stern describes it as "delicious" and "one of those things that are right under your nose and you don't expect it -- but it makes total sense." He says, "it doesn't feel arbitrary, It feels like it could have been planned all along."
- "I can tell you it's someone you've seen. It won't be a guest-star" says Ronald Moore. In producer-speak, a "guest star" is any non-regular, however Moore probably meant a brand-new guest star.
A Sci-Fi Channel promotional site, YouWillKnowTheTruth, details various clues, many possibly related to the identity of the final Cylon
- "You don't know my name." -- This could refer to characters whose full names are not known to the audience, such as Cottle or Crashdown, or to the Virtual being, whose name is entirely unknown.
- Laura Roslin's disappearance from The Last Supper may be interpreted as a sign of her death, or of her no longer being eliminated by that clue.
- The foetus with a red spine may refer to Hera, Caprica Six's unborn child or Nicholas.
- Several scenes with discussion of the Cylon God may indicate a connection to this being. We also don't know the Cylon god's name.
- Baltar's statement "seems we both made rather bad choices when it comes to our Presidential aides-du-camp, wouldn't you say?" seems to compare Gaeta and Tory Foster. His loyalties are described as divided.
- Tigh burns a picture of Ellen with his cigar, giving her a big, glowing red eye (Miniseries).
- Ellen's sudden appearance in the Fleet with no other person having a recollection as to how (Tigh Me Up, Tigh Me Down).
- Intense curiosity over specifics of quest for Earth.
- Sexual relationship with a Cavil on New Caprica.
- Ellen's appearance to her husband in visions while he is with Caprica Six.
- After Baltar declares all Cylon tests will be green, Virtual Six asks what the real result of her test was, which is peculiar as she should see what he sees. He says, "I'll never tell." (Tigh Me Up, Tigh Me Down)
- Recent return as a spirit guide may hint at a larger role. However producer's statements say she was a quick last minute replacement for Billy Keikeya. 
- Negative: She suffered greatly from exposure to vacuum with Galen, while he was not much harmed.
- Negative: Her son Nicholas has been identified by Moore as half-human, half-Cylon.
- She is in great need of redemption, given her actions.
- Hungers for redemption.
- Is the only person to hear the First Hybrid's prophecies.
The following characters are eliminated from consideration by the clues above. However for those who feel those clues are misinterpreted, the following clues exist.
- To all appearances killed in explosion, then returns two months later in brand-new Viper (Crossroads, Part II).
- Painting mandala since childhood.
- Seeks redemption for destruction of the Olympic Carrier and the death of Zak Adama.
- Told by Leoben and oracles that she has a special destiny.
- Predicted by the First Hybrid to lead the human race to its end, to be the herald of the apocalypse and the harbinger of death (Razor).
- One of the few humans to experience Cylon related visions. (Possible explanations include chamalla and blood transfusions from Hera.)
- Also apparently shares Emily Kowalski's dying vision of trip to afterlife (Faith).
- Ruled out as being one of the four revealed members in podcast for "Crossroads, Part II".
- The unboxed Three tells Roslin she is a member of the final five, then says she was joking just to see her reaction.
- Sings a song which could imply knowledge of a Cylon sleeper awakening.
- Note: His stabbing of Baltar has an unaired explanation.
- Negative: David Eick stated that they debated whether Gaeta or Anders should be one of the four revealed Cylons for some time, suggesting he is not the fifth.
- Survives a nuclear explosion that destroys his home, essentially unscathed (Miniseries).
- Frames Aaron Doral as a Cylon, who then turns out to be one (Miniseries).
- The Hybrid declares him "The Chosen One" and said he had "A mind that burns like fire." The secrets of the Temple of Five are only to be revealed to that chosen one (The Eye of Jupiter).
- Has a Six in his head that claims to be an angel from God, as well as a Virtual Baltar similar to Caprica-Six's.
- Seemingly able to cure a boy of viral meningitis by praying, as instructed by Virtual Six (He That Believeth In Me).
- Seen as the messiah by a cult.
- Unconsciously knows what part of Cylon base to attack (The Hand of God).
- By a considerable margin, the (living) character most in need of, and hungering for redemption, considering his role in the downfall of mankind.
- Often hopes that he is a Cylon; has stated he would find redemption in learning he is a Cylon.
- Cylons are uncannily attracted to him, and three of the four female models have had sexual relations with him.
- After Number Three sees image of Final Five in Temple of Five, she declares to him "So beautiful. You were right." The primary thing he has been insisting to her is that he may be a Cylon.
- Declared to be one of the smartest Colonials alive. Genius ability with computers. Demonstrable ability to cover up his background (Taking a Break From All Your Worries).
- Declared to be the father, with her, of the new hybrid race by Virtual Six (Kobol's Last Gleaming, Part II).
- Appears in visions of the Opera House seen by Roslin. He also sees the Opera House in visions led by his inner Six.
- Receives special attention from D'Anna Biers after her unboxing, more than any other character (The Hub).
- An Adama by marriage, she was not an Adama when Leoben made his pronouncement (Flesh and Bone). Other clues remain inconclusive.
- Her name, Anastasia means "resurrection" and Dualla means "duo" implying a duality of some kind.
- Survives poisoning that kills most other characters who receive it (The Woman King). (Robert's statement that he did not harm her suggests that she may not have been poisoned.)
- One of the few to experience Cylon related visions (in the room with First Hybrid) (Razor, extended version).
- Negative: Ruled out as being one of the 4 revealed members in podcast for "Crossroads".
- Seeks redemption over fear he started the war (Hero).
- Although Conoy may well be lying in order to confuse Roslin in "Flesh and Bone", it appears most likely that he refers to William Adama.
- Described as "in his father's shadow" by Romo Lampkin.
- Negative: Orders destruction of Temple of Five, which Final Five member Tyrol is unable to carry out.
- Seeks some redemption for the destruction of the Olympic Carrier.
- Lee Adama's query "What if it had been Zak in that Viper?" may also subtly refer to himself.
- Negative: The game of hostage brinksmanship with D'Anna Biers (Revelations) seems highly unlikely if she knows him to be the final Cylon.
More Speculative Options
Most highly speculative options are ruled out by producer statements that the final Cylon will not be a day player or never before seen guest star. All of the company regularly profess that they believe the ending and revelation will be highly satisfying to fans.
The various Virtual beings appear to be a manifestation of some external being or beings. There may be just one being behind the vision that Baltar sees as a Six and as himself, that Caprica Six sees as Baltar and which Starbuck saw as Leoben. This "character" is both unseen and at the same time one of the most popular regular characters, most commonly appearing as a sexy Six. The being (or one of the several beings) could take the role of the final Cylon. If so, the being would appear played by regular cast members such as James Callis or Tricia Helfer, but be distinct from the characters they normally play.
- The being claims to be an agent of the Cylon God.
- The being has manipulated a considerable number of key events in the journey of the Fleet and Kara Thrace's destiny.
- When D'Anna Biers sees the Final Five, she may see the being in any form. Since Caprica Six sees the being as her lover Baltar, Biers may also have seen Baltar. This explains the profuse apology, her telling him "you were right" and her believing that there are only "four in your fleet."
- The being is the only regular character not subject to fan speculation about being a Cylon, because most fans concluded it already was a Cylon due to the form and statements of Baltar's Virtual Six. However, the being is clearly not one of the Significant Seven. This "hiding in plain sight" is a popular dramatic trick.
- D'Anna Biers speaks to Cavil of "the one who programmed us" after seeing the Final Five.
- Negative: No clear relation to First Hybrid's prophecy or Gaeta's song.
- The Cylon God is frequently referenced as a real and intervening being.
- While seemingly ruled out by D'Anna Biers's declaration that there are "five other Cylons," it may be possible that one of the Significant Seven, in particular a special one like Sharon Valerii may lead a dual existence.
- The First Hybrid states that his existence would "begin again in ways uncertain" after his destruction (Razor).
- Materials for Caprica state that there were Cylon models based on the human memories of at least three people, however Moore has stated no new characters from Caprica will appear in the series.
- The nature of the being, represented by an internal image of Leoben Conoy, who appears to Kara Thrace in "Maelstrom" is unknown.
- Original Cylon Centurion Model 0005 units not on the Guardian basestar when it is destroyed could still exist.
- The slavery of the robotic Cylons has become an important Cylon issue. Non-biological forms could be represented in the Final Five.