Self-replicating robots were scavenging robots able to increase their numbers by building new units.
The robots were capable of self replicating from available materials. They had individual intelligence allowing them to act for their own benefit. They were able to function underwater. The Sixth Doctor described them as a plague. (COMIC: The Gift)
Monektoni Shug's spacecraft crashed on Zazz's moon. A Servatron was onboard and it survived the crash. The robot began repairing the ship and creating more robots. After twenty generations, they had built their own city.
They were forced to periodically scramble when a warning alarm rang for a meteorite shower; they hid underground. Later a meteor storm came and one large meteor hit and destroyed the city, killing the robots. Professor Strut found a robot in a rock sample he took from the moon to Zazz.
On Zazz Edit
Professor Strut gave a package to the Doctor, telling him it was a present for his brother, the Lorduke of Zazz. The package contained a single self-replicating robot. The Doctor presented it to the Lorduke at a party. The robot emerged and began to create more or its kind until they swarmed the area. They took any metal they found for the creation of more robots. One robot even stole the Doctor's watch chain.