The original Silver Shield had been around since World War II. He defended Europe from the Nazi war machine, surprising many by returning back to America in one piece. He spent the next 40 or so years mopping up after the remainders of the Third Reich. He tracked the remaining criminals to South America, Antarctica and even to a base on the Moon, and brought them all to justice! During this time he had many heroes who assisted him in his crusade, including a mysterious woman who some suspected might be his daughter. It was obvious he was very fond of her, and he sought to teach her all he knew.
Just as the Silver Shield thought his work was almost done, he received word that the Nazis had opened a portal to a parallel universe... one where the Nazis won World War II!! He and his female protege quickly went to destroy this portal. During the pitched battle, the Silver Shield was caught in a battle close to the activated dimensional door. Seeing his partner in trouble, he flung his shield to protect her and then BAM!! Total whiteout!!
When his protege recovered from the flash, she found her mentor gone and the portal destroyed. All that was left was his shield. Clinging to the hope that perhaps he wasn't dead but had been shunted to the other side of the dimensional doorway, she looks for a way to bring him back.
In the meantime, she holds onto his shield and uses a unique dual-shield form of combat as the new Silver Shield!!