Cylons are a race of artificially intelligent robots originally created by Humans on Earth as far back as Year 4000 or so according to the New Shi'ar Calendar.  The Cylons more recently rebeled against the humans (around Years 11,880 to 11,900 according to the New Shi'ar Calendar) and developed a desire to exterminate the human species. 

Cylons occasionally have traveled to the Pocket Universe from the Old Universe via the Wormholes.

In one case, a planet in the Pocket Universe was taken over by an entire army of Cylon robots and renamed New Cylon