Black Mail

Golden Age Origin
Black Mail was a robot built by two Nazi scientist, using a suit of armor that was made for the tallest knight of the 13th century. It defeated the Iron Ace in personal combat, and wreaked havoc, in its attempt to assassinate key military personnel. The robot stood around 8 feet tall, possessed superhuman strength and its creators claimed that it was indestructible. They appeared to be proven wrong, when Black Mail was seemingly destroyed by a Nazi plane that crashed on it, but Iron Ace indicated that Black Mail would ultimately return, possibly stronger than before.

Golden Age Appearances
Air Fighters Comics vol. 2 #8