When Superman debuted in 1938, he ushered in a string of imitators--Batman, Wonder Woman, Captain Marvel, Captain America. But what about the many less well-known heroes who lined up to fight crooks, super villains or Hitler--like the Shield, the Black Terror, Crimebuster, Cat-Man, Dynamic Man, the Blue Beetle, the Black Cat and even Frankenstein? These and other four-color fighters crowded the newsstands from the late 1930s through...