In a distant part of our galaxy, a human civilization has extended to a group of planets known as the Twelve Colonies, to which they have migrated from their ancestral homeworld of Kobol. The Twelve Colonies have been engaged in a lengthy war with a cybernetic race known as the Cylons, whose goal is the extermination of the human race. The Cylons offer peace to the humans, which proves to be a ruse.
With the aid of a human named Baltar, the Cylons carry out a massive attack on the Twelve Colonies and on the Colonial Fleet of starships that protect them. These attacks devastate the Colonial Fleet, lay waste to the Colonies, and virtually destroy their populations. Scattered survivors flee into outer space aboard a ragtag array of available spaceships.
Of the entire Colonial battle fleet, only the Battlestar Galactica, a gigantic battleship and spacecraft carrier, appears to have survived the Cylon attack. Under the leadership of Commander Adama, the Galactica and the pilots of "Viper fighters" lead a fugitive fleet of survivors in search of the fabled thirteenth colony known as Earth.