Metal Sonic is a character in the Sonic the Hedgehog comic series and its spin-off comics. He is a robot duplicate of Sonic the Hedgehog from the In Another Time, In Another Place Zone, created by Dr. Eggman to outmatch and defeat Sonic.
Metal Sonic is identical in appearance and wardrobe to his Prime Zone counterpart.
Sonic the Hedgehog CD
Metal Sonic first assisted Dr. Eggman in his attempt to conquer the Little Planet, which involved the kidnapping of Amy Rose. This culminated in a race against his organic counterpart, Sonic the Hedgehog, in which he was heavily damaged, thought to have been destroyed.
Sonic the Hedgehog 4: Episode II
Some time later, Eggman would return to the Little Planet during its annual return, where he would retrieve and revive a still heavily damaged Metal Sonic.
When Dr. Eggman trapped Sonic's friends at the Olympics, Sonic challenges the doctor. Making an excuse, Eggman had Metal Sonic compete in his stead. Metal Sonic would subsequently engage his organic counterpart in every Olympic event until they reached the final event; the hundred meter dash. At first Sonic was too worm out to run, but after he empowered himself with the Olympic spirit, Metal Sonic was soundly defeated by Sonic and retreated with Eggman.