The Rampaging Cyborg

The Mad Cyborg is the Cyborg that destroyed the home town of Genos, murdering his family. This is a major plot point in the One-Punch Man story, and Genos' main motivation.

Appearance
The Mad Cyborg has a brief appearance during a conversation between Drive Knight and Genos. It appears to look like a humanoid robot.

History
4 years before Genos met Saitama for the first time, the Mad Cyborg attacked his home town, destroying everything and killing his family. Genos was the only known survivor. Dr. Kuseno had been tracking it down, he came to the destroyed town and met Genos.

Drive Knight claims that the rampaging cyborg destroyed his village too, and that he thus has a similar past to Genos. He did not give a specific time frame. Drive Knight tells Genos that the Mad Cyborg is a creation made by Bofoi.

It is also revealed by Dr. Kuseno that the Mad Cyborg too killed the scientist's family in one of the villages it went around destroying.

Neo Heroes Uprising Arc
After Drive Knight tolled his history about the Mad Cyborg to Genos, it is revealed no hero records have been shown to take down the Mad Cyborg and it has not shown up for a few years. It's theorised that it is most likely in sleep mode, hidden away with the rest of Bofoi's robotic creations.