Long ago, the Final Five (Ellen, Tigh, Anders, Tory and Chief) were all working on a special project which invented the resurrection technology. Earth got blown up, the Five resurrected on a spaceship and decided to head for the already established 12 colonies to warn them not to make more robots. Unfortunately, without FTL drives they take years to get there and arrive during the first Human/Cylon war. Ooops, too late. They stop the war by offering to make the skinjob Cylons for the Centurians and created the eight models of Cyclons. These eight were numbered One to Eight, and are the ones we know today by those numbers.
Except of course for number Seven, Daniel, who was murdered by the Cavil model (and whose real name is John). Daniel incidentally was extremely artistic and soulful. And hey... wasn't Starbuck's father an artist/musician, btw? I'm offering large bets here that not all the Daniel models got killed off, that one of them is Starbuck's father and that Starbuck is in fact the first Human/Cylon hybrid after all.
Meanwhile, back at the Final Five... John the first model is more than a little insane, and also traps all the Five in a compartment and pumps the air out to kill them. Wiping the memories from the newly resurrected Five, he slowly releases them (like Boomer) into Colonial life. John (as Cavil) later goes on to really fuck with the Five in their new lives. He plays resistance fighter with Anders's mob, makes sure that Ellen gets on a tranport to the fleet, messes with the Chief's head by taking his confession and telling him he's not a Cylon, pokes Tigh's eye out on New Caprica, and sleeps with Ellen. How very Oedipus.
Interestingly, Anders in his memories, also mentions beings that only they could see. Tory saw a male, Chief a female. Sounds an awful lot like Baltar's long-time companion.
Wow. Just amazed that everything lined up so well in the end. How many episodes left!?!?