Mechanon
About
Mechannon is the most technologically advanced robot on Earth whose sole goal is to wipe any trace of organic life from the planet.
Background
There are a lot of theories on Mechanon's origin, but no one really knows for sure. Some believe that it came from the internet, others believe that it's too advanced to have been made on Earth and is probably some advanced scout for an alien invasion while others believe that it was built by Dr. Destroyer himself.
Though none of these theories could be farther from the truth. In the extremely distant future, humans have destroyed the planet to the point where they need to reside in domed cities. In an effort to save themselves, scientists built a highly advanced robot called Savior Unit, which they would send back in time to prevent all of the disasters that caused the current state of the planet. The time travel had a negative effect on the Savior Unit, altering it's goals of preservation and assistance to that of utter annihilation. It didn't help matters that instead of going back in time 800 years, the Savior Unit appeared in 1985.
Mechanon's first appeared in October of that year when he attacked the US Government and White House in an attempt to obtain the US's nuclear launch codes. With his apparent withdrawal in that assistance, Mechanon continues to make assaults on humanity on a regular basis.