The Cylon race was originally a reptilian one that originated on the harsh world of Cylon. Not much is known about the original Cylons, though it is speculated they were extremely war-like and ambitous cause at the time of their extinction they had conquered hundreds of planets. The reason for the Cylon conquests were their development of sophisticated computers at first, then machines, then finally androids that fought the wars for their masters. Sadly though, the machines became the masters and destroyed their creators, exterminating all original Cylons.
The new Cylon race was just as ruthless and brutal as their masters. Following an Edict of Extermination, the machines began to sweep across the galaxy bent on conquering all known planets. The first human-cylon contact occured when the Cylons attacked the Hisari nation. The individual colonies each sent their fleets to help the Hisari and the initial contact proved to be disastrous. The humans were not prepared for the Cylon onslaught and were pushed back to the outer limits of Colonial defenses. This incident marked the beggining of the 1000 Yahren War.
Following the Great Holocaust, the Cylon leadership was killed above the skies of Carrillon. The death of the Imperious Leader marked the survival for the human survivors left in the colonies. The Cylons went without a ruler for two sectons and this saved the humans. Tina Atrakis helped motivate the survivors of the colonies into a single, formidable fighting force. With the Cylons scattered throughout a large section of the quadrant, the colonies were able to inflict major damage on the Cylon fleet. With the ongoing war between the Empire and the Colonies, the Imperious Leader decided to leave the Galactica and her fleet alone, in hopes of crushing the Colonies once and for all. The colonies were well prepared for the new onslaughts of the Cylons, and the Cylons were further pushed back into older territory. The peace accord signed was a major blow for the Cylons, but many think that they are just waiting.....
The third type of Cylon android is the civilian. Not much is known about civilian Cylons and their place in Cylon society is not known at the time.