Humanoid Cylons
Although they made only a single appearance in the original continuity (the episode "The Night the Cylons Landed" from Galactica 1980) humanoid Cylons play a major part in the reimagining. The term 'humanoid Cylon' is a description, rather than an official designation. These beings are usually just known as "the Cylons", or derogatorily as "skinjobs" or "toasters". These Cylons are indistinguishable from organic-humans due to their creation through synthetic-biology, meaning that they are made of real bones, flesh and blood rather than metal, but still possess a digital molecular-structure. In fact, some Cylons are initially programmed to believe that they are "organic" until revealed otherwise later in life. The Cylons have nonverbal ways of sharing information but do not have a hive mind, even among the identical duplicates, and are most often shown talking to one another. There are twelve distinct humanoid models in existence, which are divided into the "Final Five" that originated on Kobol, and "Significant Seven" (the latter term is only used by the Battlestar Galactica producers). The "Final Five" are unique, and are the last survivors of the thirteenth tribe. They developed the many copies of the "Significant Seven" in conjunction with the Centurions of the Twelve Colonies. Each copy shares basic traits with the rest of their model, but they can develop into distinct individuals.
Cylon society is made up of the seven surviving known, mass-produced humanoid models - Numbers One, Two, Three, Four, Five, Six, and Eight. The Number Seven model (the "Daniel" series) was destroyed by the Number One model (the "Brother John Cavil" series) decades prior to the destruction of the twelve colonies. The Final Five were killed, and temporarily boxed, by Number One, who then purged their memories and sent them to live among the humans. The remaining six models had no knowledge of the Final Five's identities, presumably blocked by Brother Cavil, though they were aware of the existence of five absent models not to be spoken of. When D'Anna (Three) attempts to learn their identities, her entire model's line is boxed — indefinitely deactivated with their memories permanently downloaded into cold storage — as punishment by Cavil (One). In the final episode of the third season, four of the final five are revealed to be "human" characters with long histories on the Galactica. Their purpose, and how and why they were hidden from the rest of their kind, is a major plot point of the fourth and final season. In the fourth season, Ellen Tigh is revealed to be another of the "Final Five".
The humanoid Cylons are responsible for command decisions. While the command structure has not been fully explored, some hints at organization have been revealed. At the end of the mini-series, a group of Cylons are debating what to do, and one speaks authoritatively, to which another responds, "by your command", a reference to the original series. Other forms of Cylon, such as the Centurions, the Raiders and the Hybrids, appear to have little or no policy-making role within their society to the point that the humanoid Cylons can freely impose blocks on their behavior and cognitive programming. Although the Cylons consisted originally of early-model Centurions fighting for freedom from slavery by humans, by the time of the series they are entirely subservient to their own humanoid creations. Later in the series, these restrictions are loosened within the "rebel" Cylon group; Centurions are occasionally depicted as resisting authority.
In the episode "Precipice", a Cylon council (made up of multiple copies of several models) appears to cast votes collectively by model, indicating that model plays an important role in the hierarchy of Cylon society and that they always make decisions in this fashion, as Cylons of the same model are implied to have higher or lower ranks than Cylons of other models at various times. It was also shown during the occupation of New Caprica, that a select group of humanoid Cylons, mostly ones who had been within the Colonies, such as Boomer and Caprica Six, seemed to have seniority within their own model. One of each model was seen deliberating and discussing their course of action, with each of the 'senior' copies representing the opinion of their entire model group. The Number Ones subvert consensus by undertaking many actions without the knowledge or consent of their siblings, such as turning against the Number Sevens and the Final Five, and then reprogramming their siblings to hide this.
Although little is known about Cylon psychology, it is clear that they share many of the same emotional vulnerabilities that humans possess. This is evidenced by Gina's catatonic state as a result of the severe trauma of her abuse at the hands of the Pegasus crew. This abuse was presented in the form of multiple sexual assaults, battery, starvation and outright torture. Number Six/Caprica Six also revealed that Cylons exist by 'projecting' an environment of their choice on the real/physical world.
Read more about this topic: Cylon (reimagining)