From The Mega Man Universe
Shield Sheldon is a Reploid modeled after a shellfish. He was created by Gate and his purpose was to serve as a bodyguard for important people. He was renowned for his excellent protection of chiefs of various research institutes. In one incident, however, he was charged with protecting a laser researcher named Dr. Jim. One day Dr. Jim turned Maverick, and Sheldon had no choice but to dispose of him. The Maverick Hunters who arrived on the scene misinterpreted what had happened, and charged Sheldon with being a Maverick for killing Dr. Jim. Under the stress of the incident and the shame of his inability of saving Dr. Jim, Sheldon was driven to taking his own life. Gate later revived Sheldon as a member of the Nightmare Investigators and sent him to the laser research institute.
Shield Sheldon uses the large, protective shells he carries both offensively and defensively. He can throw both shells, which come back to him. He can also create a copy of himself and both will swing their shells at their opponent. Next, he can retreat into his shells and bounce around the room. His more powerful attacks involve surrounding himself with Guard Shells, and sending his shells to the four corners of the room and jumping from one to the other.
Shield Sheldon is another tragic story in the series. He was very loyal to those he served, as well as very prideful of his work. As Gate had revived him, he saw it as his utmost priority to protect him.