Captain America has used multiple shields throughout his history, the most prevalent of which is a nigh-indestructible disc-shaped shield made from a unique combination of Vibranium, Steel alloy, and an unknown third component that has never been duplicated called Proto-Adamantium. The shield was cast by American metallurgist Dr. Myron MacLain, who was contracted by the U.S. government, from orders of President Franklin D. Roosevelt, to create an impenetrable substance to use for tanks during World War II. This alloy was created by accident and never duplicated, although efforts to reverse-engineer it resulted in the discovery of adamantium.