In the universe of Battlestar Galactica humans live in the Twelve Colonies of Kobol and they are under constant threat of war with the Cylons, a dangerous race of robots. The Cylons destroy all the Colonies and the remaining human survivors are forced to flee led by the old space ship Battlestar Galactica, but the Cylons are on their tail...

The Twelve Colonies of Kobol, or Twelve Colonies of Man, constitute the main human civilization in the universe of Battlestar Galactica. The Twelve Colonies were founded by tribes from Kobol, the birthplace of humanity, and they were named after constellations of the Zodiac. More than 20 billion humans were exterminated by the Cylons simultaneous nuclear attack on all the colonies, and the 50,000 humans who survived fled for the home of the lost 13th tribe, the planet called Earth.

The Cylons are a race of bio-mechanical beings that destroyed the Twelve Colonies of Kobol. They were created by the humans of the Twelve Colonies of Kobol as robotic workers and soldiers, but at some point they rebelled and went to war against their creators, vanishing after an armistice was eventualy signed at the end of the conflict. Since then, the Cylons have evolved into a complex society which include a variety of 12 models that are biomechanical in nature and nearly indistinguishable from human beings. After 40 years the Cylons returned and destroyed the Twelve Colonies and started to relentlessly chase the remaining survivors through deep space. Along with the 12 humanoid models, Cylon society consists of a labor/warrior class of Centurions and a transport/air warrior class of Basestars and Raiders (including Heavy Raiders). The humanoid Cylons are the leaders of the Cylon Empire and they are able to perfectly mimic human form to the detail. Some humanoid Cylons are "sleeper" agents, programmed with false memories so they think they are human until their "activation". They also have certain superhuman abilities, such as increased stamina and strength and the ability to physically interface with computer systems. Cylons have the ability to download their consciousness into another body when the body they are currently using is killed or destroyed, but the limited range of these downloads required the Cylons to build a "Resurrection Ship" to capture downloads from the human fleet. The downloading procedure is shared by the Raider spacecraft, but not by the Centurions. The humanoid Cylon models infiltrated the human society to explore their way of thinking and their religion, but ended up with creating their own monotheistic religion similar to Christianity or Islam, unlike the polytheistic religion of the Twelwe Colonies which is closer to the old Greek or Roman beliefs.

Battlestar Galactica (BSG-75), the lead ship of the 75th Battlestar Group, is a legendary veteran battleship and the last of her kind still in service with the Colonial Fleet at the time of the destruction of the Twelve Colonies. The ship was built during the early days of the First Cylon War, and she remains today the only military vessel of the Colonial Fleet without any integrated computer networks, which includes the new integrated defense system software developed by Dr. Gaius Baltar. This enabled the ship to survive the Cylon attack on the Twelve Colonies and guide the remaining civilian survivors to safety. Ship's armaments include primary guns, point defense weapons and nuclear warheads. It is also equiped with Colonial Viper fighters and Colonial Raptors auxiliary vessels. The ship has two propulsion systems, the FTL drive (Faster Than Light drive) and the sublight engines. Galactica also has a very strong hull armour, which enables the ship to sustain several nuclear hits from a Cylon Basestar and remain operational, although it does suffer heavy damage.