Buzzsaw (also known as Metal Sonic v1.5) was a robot created by Eggman Enterprises for the sole purpose of stealing the Master Emerald and destroying Sonic. He is the secondary antagonist of Sonic 3: The Story of Knuckles, and the successor to Mechhog.
Buzzsaw was a robot designed by Eggman Enterprises as a successor to it's previous model, Mechhog. Buzzsaw (called Buzzsaw 2 by Sonic) gets his name from Sonic's nickname for Mechhog, Buzzsaw. Buzzsaw was developed to steal the Master Emerald from Angel Island and kill Sonic the Hedgehog. He was designed to look more like Sonic, unlike his successor, Metal Sonic.
Buzzsaw stole the Master Emerald from Angel Island and caused the island to sink, and then distracted Knuckles long enough for him to be captured by Dr. Eggman. However, Sonic and Tails destroyed him on the Death Egg and freed Knuckles, who worked with them to put a stop to Eggman.
Buzzsaw is a cold, lifeless, and ruthless robot who only takes orders from his creator, and will do anything necessary to achieve what he is directed to do.