Louise Grant was a secretary to O.S.S. agent Mark Mason, who ran a private detective agency. Enamored with her boss and wanting to help him break cases, she surreptitiously donned a floor-length red evening gown, black domino mask, and high heels, and ventured out at night fighting crime as the costumed crimefighter the Blonde Phantom. Mark developed a romantic interest in the Blonde Phantom, but continued to not notice Louise, apparently oblivious to the fact that they were both the same woman.

Louise is a normal human woman with no super powers. However, during the brief body switch with She-Hulk, Louise temporarily gained superhuman strength, stamina, durability, and a regenerative healing factor.