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1. THE BEGINNING
Cylons were machines created by weapons technologist Dr. Daniel Greystone to serve in the military. The artificially intelligent automatons eventually came to serve humans, like slaves, on the planetary system known as the Twelve Colonies of Kobol.
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2. THE UPRISING
The Cylons rebelled against their masters. Man and machine engaged in a long and bloody war. The Colonies defended themselves with large, aircraft-carrier ships called Battlestars.
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3. THE FINAL FIVE
During the war, the Cylons encountered the last five members of a distant, highly evolved race of Cylons, who resembled humans in practically every way: Saul Tigh (Michael Hogan), Galen Tyrol (Aaron Douglas), Tory Foster (Rekha Sharma), Ellen Tigh (Kate Vernon), and Samuel Anders (Michael Trucco).
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4. THE RESURRECTION
The Final Five struck a deal with the robotic Cylons: We can make you look human, and give you a technology that allows you to download your consciousness into a new body if your current one should perish, making you essentially immortal. But the cycle of violence must stop; you have to end the war with humanity. The Cylons agreed.
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5. THE NEXT GENERATION
The Cylons disappeared for 40 years, perfecting their human replicas with the Final Five's guidance. They made eight distinct models, but in a fit of jealous rage, the first model — known as Cavil (Dean Stockwell) — completely eliminated the seventh model, the Daniels, bringing the total humanoid Cylons to 12.
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6. THE ERASURE
Unlike the Final Five, Cavil believed humanity still needed to pay for enslaving Cylons. To keep them from interfering with his plans, he wiped the Final Five's memories, and placed them among the Colonies to live as humans. Saul joined the military, eventually serving under his longtime friend Commander William Adama (Edward James Olmos) on the Battlestar Galactica, and Ellen remained Saul's boozy wife. Galen became a noncom chief engineer on Galactica. Anders turned into a pro sports star. And Tory joined politics.
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7. THE INFILTRATION
Cavil then placed multiple models of the remaining seven humanoid Cylons as sleeper cells in the Twelve Colonies. One, a model Six (Tricia Helfer) and a firm believer in the Cylon's one true God, infiltrated the human defense mainframe by infiltrating the bedroom of scientific genius, and unrepentant horndog, Gaius Baltar (James Callis).
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8. THE GENOCIDE
The Cylons struck, killing billions of humans in the Twelve Colonies.
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9. THE PURSUIT
The last 50,000 members of humanity, led by the Galactica, limped into the cosmos, looking for a fabled planet known as Earth — inhabited, so humanity's polytheistic scriptures say, by the lost 13th tribe of humans. The Cylons relentlessly pursue the human fleet, where several of the humanoid Cylon models were still hidden. Miraculously, all of the Final Five also managed to survive the Cylon attack, and they too ended up in the human fleet.
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10. THE CHILD OF DESTINY
One humanoid Cylon, a number Eight (Grace Park) known as Sharon ''Athena'' Valerii, fell in love with hunky human Karl ''Helo'' Agathon (Tahmoh Penikett). They got horizontal, and had a baby, Hera: The first human-Cylon hybrid. Outed as a Cylon, Athena ultimately won Adama's trust and joined the human fleet as a pilot.
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11. THE AWAKENING
At a particularly grim time for humanity, Saul killed Ellen for being a Cylon sympathizer. (Ironic, no?) When she was resurrected, she remembered everything, and Cavil kept her captive on a Cylon Basestar. Meanwhile, Saul, Galen, Anders, and Tory eventually realized they were Cylons — thanks to an eerie version of ''All Along the Watchtower'' ringing through their heads — but they all kept it a secret.
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12. THE REVEAL
When the human fleet finally found Earth, instead of an Eden, it was a wasteland unfit for any life, irradiated some 2,000 years previous in a massive nuclear holocaust. It was familiar territory, however, for the Final Five: Turns out, they are Earth's only survivors. Yup, the 13th tribe of humanity were, in fact, all frakking toasters. Whoa.