The Emperor Metallix first appeared as Metal Sonic and attempted to obtain the time stones for Robotnik but was defeated by Sonic.
He later was rebuilt into his current design as a giant red Metallix that sat on a hover throne, he was another dimensional counterpart to Mega Metal Sonic.
After trying to take over the world due to thinking that the Metallix were perfect, he and his army were defeated.
His last physical apperance was when Supreme High Robotnik summoned him in his Metal Sonic form to fight alongside the other villains.
He later appeared as the main antagonist of the Sonic Generations Sonic the Comic Story.
His latest apperance he was rebuilt again into a much more powerful variant, the Neo Metallix.