#sonicchaosseries

So basically, in his timeline, he was captured by GUN to use his powers to further their agenda, forming him into a GUN agent. However, being a rebellious teen, he ended up breaking free and deciding to do his own thing. To get him back, GUN "got rid of" all of the people he'd gotten close to and, when he continued to rebel against them, they mortally wounded him and left him for dead to show him what happens when you refuse to listen as one of their agents. Enter the main timeline's Eggman, who comes in and sees him. He promised him revenge, a second chance at life, the opportunity to be his own person and, when the kid agreed, took him back to his timeline. So Eggman sees that he's got the perfect opportunity to create a robot capable of not only rivaling, but potentially surpassing Sonic. So he slowly turned him into Metal Sonic, using "I'm saving your life from your mortal injuries" and "Oh, it looks like your robotic parts are going to sap your life away if I don't add to you" as reasons why.

Anyway, here's Pre-Metal Sonic.