Mary Zero was a mutant that possessed a mutant gene that made her virtually invisible to those around her. She formerly existed outside the visible and audible perceptions of most human beings. Those few people that did interact with Mary were typically affected by short term memory loss which made them forget about her. Animals were able to perceive her. Agent X was they only human who seemed able to perceive her.
The teenage girl known only as Mary Zero Possesses an unusual mutant ability which makes her invisible and inaudible to human beings, living unnoticed in people's homes and stealing food and goods from stores. On her birthday, Mary went to rob a jewelry store, coincidentally, at the same time as a group of professional thieves. Mary managed to slip into their getaway car unnoticed; however, they were pursued by Agent X (Alex Hayden), who forced the car off the road. Agent X stopped to see if Mary was injured and when she realized that he could see hear and remember her, she instantly became smitten with him. Mary Zero accompanied Agent X as he clashed with the assassins of the Four Winds; when a bullet lodged in his throat and nearly killed him, Mary was distraught at her inability to summon help, though he eventually recovered. To bring an end to the attempts on his life, Agent X had Mary walk into the Four Winds' offices and retrieve files on their members' families and mistresses, using the information to blackmail them. Hayden soon formed Agency X with his mercenary friends and Mary Zero who promised to stay with him. However, when the Scarlet Witch warped reality, depriving many mutants of their powers, Mary Zero was among those affected; her abilities were made part of the being called the Collective.