The Mechanical Men are a species of very small robots from the planet Industro. They have described themselves as super-intelligent, corrosive-resistant and self-oiling, and are also quite powerful despite their small size.
They have a fundamentally hostile mentality, seeking to conquer worlds by brute force, and they believe a leader should be ruthless and cunning. Their technology is highly advanced and they are capable of some amazing feats, such as altering the minds of other beings, transferring character traits from one mind to another
A legend dating back to ten thousand years ago stated that a great warrior would come to lead the Mechanical Men into a new age of glory and galactic conquest. They believed that the Robot B9 from the Jupiter II was that leader, and went to Gamma VI in order to "rescue" him from the Robinsons. Seeing that the Robot displayed undesirable qualities such as kindness and compassion, they opted to transfer to him some of the worst aspects of Dr. Smith's personality, causing the Robot and Smith to basically switch nature. Lead by their new ruler, the Mechanical Men attempted to take the Robinson's ship by force, but were defeated and retreated after a laser blast caused the Robot and Dr. Smith to revert to their former selves.
- Lost in Space - S02E28 - "The Mechanical Men"