Metal Sonic

Metal Sonic 2.0 was a version of Metal Sonic created by Dr. Eggman. Modelled after the original Metal Sonic, this version lacked the former's cunning and ruthlessness. Nevertheless, Metal Sonic proved to be loyal to Dr. Eggman and, to an extent, effective against Sonic the Hedgehog. Numerous versions of Metal Sonic have been produced by Eggman, as the previous versions have subsequently been destroyed by Sonic and his allies.

First Model
When the Freedom Fighters and Shadow the Hedgehog found a lost military base from before the Xorda attack, Dr. Eggman constructed Metal Sonic and sent him to investigate, as well as engage Sonic in combat. (StH: #146)

Sonic, Metal Sonic and Shadow all got into a three-way brawl upon meeting up, with the latter two eventually teaming up against the blue blur. When the three were separated, however, Metal Sonic found himself conversing with the base's caretaker, Isaac, about the history of the instillation and Mobius itself. (StH: #147, #148)

When the three started fighting again, they stumbled upon an ancient missile that Isaac was about to launch. The missile was stopped by Shadow and Sonic, and the new Metal Sonic was defeated and destroyed. (StH: #148, #149)

Second Model
Following this encounter, Shadow located the facility on Prison Island where Professor Gerald had finished creating him and was last seen alive. There, a replacement model of the destroyed Metal Sonic suprised and engaged Shadow in combat. The two were rendered unconscious when Metal Sonic fired a super charged weapon that caused a major explosion nearby. Eggman's "daughter" Mecha retrieved the damaged Metal Sonic and brought him back for repairs, while also bringing Shadow with her. (StH: #157)

Some time later, Metal Sonic soon captured Sonic and brought him to Dr. Eggman, who used a device to control Sonic's body. When Metal Sonic went into some sort of stasis, Snively, frustrated with Eggman's childlike methods of defeating Sonic, decided it would be a good time to betray his master once again. When he attempted to reprogram Metal Sonic to work for him however, he found that it was spying on him. Eggman revealed that he knew of Snively's treacherous ways, and programmed Metal Sonic, along with every other robot, to monitor Snively in case he decided to back stab Eggman once again. When Knuckles destroyed the device in Sonic's ear, Eggman and Metal Sonic attacked Knothole Village, but Metal Sonic was easily destroyed by Sonic, Tails, and Knuckles. (FCS)

Third Model
A new model was produced and used to attack Freedom HQ. Unlike previous models, this Metal Sonic allowed Dr. Eggman to speak through it. When Scourge the Hedgehog explained to Eggman that he and the Suppression Squad had taken over Freedom HQ, Eggman simply had the new Metal Sonic attack him. Sonic arrived on the scene shortly afterwards, but Scourge decided he preferred to fight alone and not get help from Sonic. Metal Sonic then proceeded to attack both Scourge and Sonic, and reinforcements arrived moments later in the form of Metal Scourge. While proving evenly matched against their organic counterparts, both Metal Sonic and Metal Scourge were quickly destroyed by the Suppression Squad. (StH: #191, #192)

Fourth Model
Shortly after the destruction of both Metal Sonic and Metal Scourge by the Suppression Squad, Eggman created a new Metal Sonic model, this time using the newer SXSU-40 engine instead of the typical STH-25, allowing the robot to transport to any other dimension to pursue Sonic. Metal Sonic was then sent to Moebius and attacked Sonic and the others in Castle Acorn. Sonic asked Metal Sonic to help him kill Scourge, instead of attacking everyone else. (StH: #195)

Background Information
Interestingly, another Metal Sonic was seen being built in the background when Espio was sneaking through Eggman's base. It can be assumed that this is the Metal Sonic later used to attack Scourge at Freedom HQ (StH: #174, #191)