Berserker

[Berserkers][1]: Relentless, remorseless, pity less, tireless, adaptive, cunning, self replicating, artificially intelligent, genocidal doomsday weapons of a long forgotten interstellar war between two extraterrestrial races known as the Builders (the Berserker creators) and their enemies the Red Race (both now extinct). Berserkers have only one programmed directive and purpose "Destroy all life." Ranging in size from approximately human (in the case of assassins and spies, which are rare) to minor asteroids (in the case of repair bases) they are typically large and roughly spherical space vessels. If one approaches your planet, MOVE OUT NOW!

The only known source of help has been a particularly cunning and vicious race known a Homo Sapiens; who have had some success in defeating the Berserkers, though their results are somewhat mixed and they can betray their own species and become known as "Good Life."

[1]: en.wikipedia.org/wiki/Berserker_(Saberhagen)