Ok. After reading your previous response and discovering that Metal and Silver Sonic are supposedly two different entities, I headed to the profiles of the characters. I read through them, but I'm still confused. I thought Metal Sonic was the name for the character in Sonic 2 that comes back in Sonic & Knuckles which Knuckles then defeats. Now I see that that was really Silver Sonic. But why would Dr. Eggman build 2 robotic Sonics? I thought they was only one.
There are three robotic Sonics in the SEGA Sonic version. The original Silver Sonic, which appears in Sonic 2, the Silver Sonic MKII which appears in Sonic and Knuckles, and the Hyper Metal Sonic which appears in Sonic R, Sonic CD, and Sonic Adventure just to name a few.

To explain Silver Sonic was made in Sonic 2 to be a boss, but being beaten so easily Robotnik redesigned it to the Silver Sonic MKII. It's believe to be a remake because they both have the same basic moves and attacks. The Hyper Metal Sonic was made to be the ultimate Sonic robot matching speed and strength. - Ron Prower