Metal Sonic (メタルソニック Metaru Sonikku?) is the secondary antagonist in the Sonic the Hedgehog series. He is an evil Badnikversion of Sonic the Hedgehog and undoubtedly Dr. Eggman's greatest creation, built for the sole purpose of destroying Sonic. Deployed during Eggman's operations on Little Planet, Metal Sonic confronted Sonic in battle and lost, though he would return again and again to challenge Sonic and his allies. Modeled with extreme accuracy after Sonic, Metal Sonic not only resembles his template, but can also imitate his moves and achieve velocities matching Sonic's.
While mostly serving as Eggman's obedient and quiet enforcer, Metal Sonic is an intelligent machine with a very dark side. He is a cold-hearted, aggressive and ruthless killer with a obsession of Sonic that surpasses his maker's, and his ultimate goal is proving to Sonic that he is the better of them and eliminate him once and for all. His mission has made him rebel against Eggman and amass immense power multiple times, only to always fail in the end. To this day, Metal Sonic continues to be one of Sonic's most formidable foes.