Metallix is the Sonic the Comic incarnation of Metal Sonic, a major protagonist in the Sonic the Hedgehog series. Metallix has quite a different history to its video game counterpart: it was originally invented by Grimer Wormtongue, faithful lackey of Dr. Robotnik throughout STC's run and an entire army of them was created instead of just one.
The Original Metallix[]
The first Metallix Badnik appeared during STC's Sonic CD tie-in, and was linked to the mechanized Miracle Planet that Robotnik had conquered and was intending to use as his new base. Metallix kidnapped Amy Rose - one of Sonic's team of Freedom Fighters - and used her to lure Sonic into a trap. Sonic followed the Metallix to the Miracle Planet and they fought, but the fight was interrupted by a shrunken version of Sonic from the future. The future Sonic shrunk his past self using a shrink ray and gave him a Time Stone so that he could travel to the past and stop Robotnik's machinery from taking over the planet. Sonic used the Time Stone and arrived in the past just as Robotnik's mechaforming machine had begun its task. Sonic was shrunk down so he could get inside the machine and destroy it from within, and he succeeded in this task and travelled back to the future to repeat previous events. As the timeline reasserted itself, the Miracle Planet returned to normal since Robotnik's machine never grew to cover the planet. This resulted in Metallix - which was sustained by the planet's energy - being erased from existence.
The Brotherhood of Metallix[]
Though the original Metallix was gone, more would take its place. Dr. Robotnik would later abandon his Egg Fortress base in the Special Zone and leave his Metallix Project to run on its own and create the ultimate Metal Sonic. The operation went rogue, however, and the Brotherhood of Metallix was born.
See Brotherhood of Metallix for more details.