Cylons are a fictional, extinct race of reptiles and the cybernetic civilization that replaced them in the Battlestar Galactica science fiction in the original 1978/1980 series. They are at war with the Twelve Colonies of humanity.
Cylon society is composed of six models, four of which have been well-documented. All Cylons, from the IL-series down, typically repeat the phrase "By Your Command" when responding to any order.
Imperious Leader is the leader of the Cylon Alliance and highest Cylon model. The Imperious Leader is an IL-Series Cylon with some extra augmentation, including a third brain and a body shell resembling the reptilian Cylons. One was killed at the Battle of Carillon and another was likely killed during the Battle of Gamoray. The voice of the Imperious Leader is almost always identical to that of Count Iblis (both were voiced by Patrick Macnee).
In the Galactica 1980 episode "Space Croppers", Dennis Haysbert was the new voice of the Imperious Leader. It is stated in the original novelization of the pilot episode that the Imperious Leader's third brain is specifically designed to emulate the human mind (solely for the purpose of anticipating human actions).
An IL-series Cylon acts as a commander for the military and governor for civilians of the Alliance. They have two brains, a humanoid face and wear shimmering cloaks. They are almost feudal in nature and bicker among themselves frequently. IL-series Cylons have an effete human-sounding voice, unlike the flat mechanical tones of Centurions. They pride themselves on having two brains, as opposed to the single brains of Centurions. The IL-series also have two "eye" scanners as opposed to the one scanner of the Centurion model.
Command Centurion: Centurions with gold armor. These are the lower commanders for individual military units. The most well known Cylon character of this model is Commander Vulpa in "The Gun on Ice Planet Zero". Their voices are slightly different (lower pitched) than regular Centurions.
In the novelization of the original series it is stated that there is an elite class of Command Centurians, roughly equivalent to feudal Counts, which act as executive officers to the Imperious Leader and are not subordinate to the IL-Series, and like the IL-series they were also said to have multiple brains. In the TV series these are actually seen on screen, though very rarely, and are distinguished from other Command Centurians by black bands on their gold armor. Vulpa was originally of this class but had been demoted and stationed on ice planet Arcta.
Military androids with silver armor. Basic centurions make up the ground forces and pilots of the Alliance military. Centurions are armed with a powerful energy weapon, often referred to as a blaster rifle. They also have bayonets and swords for close combat and execution of prisoners. (Although Earth's Roman Centurions commanded a unit of eighty men, Cylon Centurions form the rank and file of the Cylon forces.) There are four Centurions that are given names in the series: Flight Leader Serpentine from "Saga of a Star World", Centuri from "The Night the Cylons Landed", Red Eye from "The Lost Warrior" and Cyrus from "The Return of Starbuck", although the last two were names given to crashed Cylons by humans.
The Cylon Centurions – the type most often depicted in the original Battlestar Galactica – were strikingly similar to the Imperial stormtroopers of Star Wars. The similarities were noted by many at the time and may have been one of the factors that prompted 20th Century Fox's lawsuit for copyright infringement against Universal Studios, the owners of Battlestar Galactica. The lawsuit was eventually dismissed as "groundless."
There is also a unique Cylon with glittering robes, with what looks like a mask attached to its face. They are seen in the Imperious Leader's delegation to Gamoray in "The Living Legend". This is evidently some kind of civilian Cylon, as Gamoray is said to have a very large community of civilian Cylons, though how civilian Cylon society differs from its military is never explored.
A Cylon android is featured in the Halloween episode of Galactica 1980. Named Andromus, this model has a superficial human appearance and a condescending attitude toward Centurions, and it is believed to be entirely mechanical beneath its artificial skin.
Cylons employ several spacecraft models, such as


In the 1978 Galactica movie and series and the 1980 spin-off, the Cylons were created to serve the reptilian race of the Cylon Alliance.
Cylons are robots created by an extinct reptilian race, as related by Apollo in the premiere episode. As a reminder of their reptilian roots, some advanced Cylon models keep large lizards as pets, as glimpsed in several scenes. In the episode "War of the Gods", Count Baltar mentions that he recognizes Iblis's voice as that of the Cylon leader, and Iblis counters that if that was true it must have been "transcribed" over a thousand yahren (years) ago.
At the beginning of the series the Cylons are singularly devoted to the destruction of humanity. The war started when the Cylon empire sought to expand into the territory of the Hasaries, and the Human Colonies intervened on behalf of the conquered Hasaries. Due to those events, the Cylon empire now viewed the entire human race as a target.
Cylons are led by the Imperious Leader, an IL-Series Cylon elevated to a supreme leadership position over all Cylons. The Cylon Empire is also responsible for tributary powers under the aegis of the Cylon Alliance. The Ovions (an insectoid race enslaved by the Cylons and transported to the planet Carrilon for mining purposes) are the only known member of the Cylon Alliance shown onscreen, other than the Cylons themselves. This may be due to the fact that the Cylons rarely maintain alliances for longer than is necessary for efficiency; they regularly turn on and exterminate their living allies when it suits them.
Cylon society is almost exclusively military. Until the discovery of Gamoray, which the Colonial fleet had targeted for its rich fuel reserves, no civilian Cylon outpost had ever been seen by anyone.
Presented in The Gun on Ice Planet Zero book, multi-brain status is presumed to be the upgraded inclusion of an auxiliary brain unit, allowing for higher-level thinking abilities. The command centurion and garrison commander on planet Tairac, Vulpa, demonstrated this ability.
In the Maximum Press comic, the Cylons were originally led by a ruthless, conquest and expansionism-driven emperor named Sobekkta, one of the original living Cylons, who were a race of intelligent reptiles.