Don't confuse "Cylon" with "Final Five"
The original Cylons (the 7 humanoids and the metallic ones) first defined the concept of Cylon in this version of BSG. Now the writers call them the Significant 7 or S7. The audience has been introduced to the concept of the "Final 5" Cylons. Because they are both called Cylons, I often see people confusing the two, and making some very wrong assumptions about the final 5. These are two very different types of Cylon, with two very different agendas. More different than any two factions of humanity in history, so it's hard to get a grasp of it. Strictly speaking only the S7 are descended from Graystone-brand Cylon(TM) Robots, but "Cylon" has become, like Aspirin, the generic term for an artificial being in the show.
The name "Final Five" which is Baltar's name for the last 5 Cylons he would meet, is confusing. If you think of them as the "Original Five" that might help a bit.
Let's look at some comparisons to clarify this:
- The S7 engaged in a genocidal war against the colonies. The F5 fought for the colonial side. They played no visible part in planning or executing the Cylon attack.
- The S7 have many copies. For the F5, we've only seen one, and perhaps another in white robes in a projection of the Kobol opera house.
- The S7 seem fixed in age, and come out of the tank that way. The F5 age like humans.
- The S7 were the occupiers on New Caprica. The F5 were the leaders of the resistance.
- The S7 are super-strong and super robust. The F5 are perhaps slightly above average and not super strong until activated. (Tyrol was able to handle vacuum much better than Cally.)
- The S7 infiltrated the colonies 2 years before the war. The F5 were there at least 40 years, probably much longer
- The S7 are the result of experiments the metal Cylons did after the war. The F5 built the "Temple of 5" while on a trip from Earth, 4,000 years ago.
- Just to make that clear. The S7 are a few decades old and from Caprica. The F5 are several thousand years old, and from Earth
- The S7 fear Kobol. The F5 choose to appear in the Kobol opera house setting, destroyed 2,000 years ago.
- The S7 have built in programming commanding them not to think about the F5; trying to get past it got #3 boxed. We don't know much about the F5's programming, other than 4 were planted as sleepers, set to "wake up" at the Ionian nebula.
- The Centurions will obey and not shoot at S7 members. Before activation, they would attack F5 members. After activation, this appears to have changed.
- The S7 can't breed with one another and have a very hard time breeding with humans. Tyrol of the F5 seemed to have little trouble breeding. Tigh quickly was able to breed with Caprica Six.
- The S7 planted copies all over the colonies. We only see one of each F5 planted, but 3 (possibly 4) were arranged to be on or near Galactica at the start of the war, one as XO. The 4th made it through remarkable odds, and we don't yet know how the 5th got there. The F5 were clearly very interested in Galactica and Adama.
- The S7 worship their god from afar, and Cavil is even doubtful. The F5 appear to have been the 5 priests of some god which seems likely to have been the Cylon god.
- When the Raiders learn the F5 are with the fleet, they immediately back off -- or possibly Anders sends an unconscious command that they do so. Some of the S7 don't believe the raiders. (No cylon reacted to the F5 before activation, however.) Raiders happily attack the fleet with S7 members aboard, and even Athena who fights them.
This show has a cycle. All this has happened before and will happen again. There have been several cycles of creation of Cylons and war with them. The S7 are from the latest cycle, or believe themselves to be. The F5 are from some earlier cycle, possibly going back to the very first cycle.
There's still a lot we don't know about the F5. We don't know what their agenda is. We don't know their relationship to the Cylon god. We don't know why they were planted as sleeper agents, set to wake up at the Ionian nebula, and planted as much as 60 years ago. We don't know if there are other copies, sleeper or non-sleeper out there, at different apparent ages. We don't know how, when or why they implanted themselves in colonial society, but since they age and can have children, they have probably been there since the exodus from Kobol. We don't know if they took the same form each generation or not. We don't know how or why they (or somebody related to them) programmed the S7 not to think about them, while still knowing they exist at some level.
We can guess a few things:
- They probably knew about the war, even if not planning it, and probably allowed it to happen. Their plan involves taking the colonials to the Ionian nebula, and beyond, after all.
- The final 5 have been Cylons "from the start" according to Tyrol. That means either from birth, or embedding in colonial society as children. They could be natural born or switched in a hospital, or snuck in later with forged histories.
- They probably snuck the knowledge of their biotechnology to the metal cylons to help them create the S7, and got to control their programming at that time. This explains why the S7 are not very good at their biotech, and can't breed themselves even though they can grow themselves in tanks. (Hint: starting from a human template, which one is easier?)
- They probably come from Earth, since the Temple of Five, in which they appear, is said to have been built by the mythical 13th tribe of Earthlings. (This is mostly confirmed by the rebel Hybrid.)
- They are the disciples of some godlike figure, the god whose name must not be spoken in the temple of five. This is almost surely the Cylon god, who put a message in the babble of the Hybrid that Baltar decoded as meaning to go to the Algae Planet.
- They like Bob Dylan. :-)
- They make be interested in the Adamas because Joseph Adama, father of Bill, helped Graystone to build the first Cylons, and Bill's big sister Tamara was the template for one of them. Later J. Adama renounced the project, and may have opposed the slavery of the Cylons.
- Even before full activation, they had some compulsions, like Tyrol's quest to seek the Temple of 5 and his refusal to destroy it when ordered.
They have entirely different agendas. While Tigh had a daydream about shooting Adama, truth is, there is no reason an F5 member would want to kill Adama. If one group is controlling the other, it's the F5 who are manipulating the S7.
So if you hear the word Cylon, be sure to realize that there are at least 2 very different types, and you can't assume almost anything you learned about one type is true of the other.