Humanity lived on twelve colony worlds in a far distant star system.
They fought a thousand-year war with the Cylons, war robots created by a reptilian race which expired long ago. Having never been commanded to cease fire, these war robots continuously waged war against the colonials.
Mankind was defeated in a sneak attack on their homeworlds conceived by these robotic servants, now referred to as Cylons, and carried out with the help of Baltar (John Colicos).
Protected by the last surviving warship, a Battlestar called Galactica, the survivors fled in any ship that could fly. The commander of the Galactica, Commander Adama (Lorne Greene), led this "rag-tag fugitive fleet" in search of a new home on a legendary planet called Earth.