Sergeant Robin Marshall was a UNIT soldier. He was guarding Vault 75-73/Whitehall when the Mim inside escaped. Sergeant Marshall was killed in the ensuing conflict. The Mim merged with Marshall's body and later reconstituted itself, taking the dead Sergeant's form. It went to visit Liz Shaw, who figured out that it was not the real Marshall. (AUDIO: Shadow of the Past)
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