Andrea was the daughter of Carl Beaumont who was forced into the debt of Gotham City mob boss Salvitore Valestra. During her life her mother died, after which she spent a lot of time at her graveside talking to her which led to her first meeting with Bruce Wayne. The two quickly fell in love with Bruce proposing to her,however she was forced to break it off and live to Europe with her father for their own safety. However this eventually failed when Valestra sent his premiere hitman after them who murdered Andrea's father, she then set out gaining the equipment needed for her revenge. Years later Andrea returned to Gotham City where as Phantasm she began killing off those involved in her father's death, although this accidentally had the Blame shifted to Batman who the GCPD set out to capture. Although Andrea did play a part in rescuing an injured Batman from being captured with the two briefly renewing their relationship.
Although they clashed when Andrea learning that the hitman who had killed her father was now the Joker,she sat out to find him at his hideout at the abandoned Gotham's World Fair. However the Joker prepared almost killed her until her rescue at Batman's hands, with the two arguing over the fate of the Joker as the World Fair began crashing down around them. While unable to reach them Batman was forced to flee, as Andrea and Joker disappeared into a cloud of smoke into the sewers. During which Bruce's words led to a moments hesitation which allowed an explosion to separate the two. She then returned to the Batcave leaving a locket for Bruce letting him know she was alive before she departed from Gotham for three years.
During which she traveled the world where as Andrea she acted as a go-between between a client and Phantasm who would frequently worked as a Spy, Thief or Enforcer. During this period she was approached about the assassination of Bruce Wayne, which she refused before returning to Gotham City, where she warned Bruce before being captured by Kitsune and several armed men.She then came face to face with Arthur Reeves who had put out the fake hit to draw her back to Gotham to kill her in revenge as he blamed her for his jokerized grin. However he was prevented from this by Batman. During the melee Arthur knocked out and unmasked Batman. Andrea, desperate to protect her love, manipulated Arthur into falling from a building, killing him. Andrea used Kitsune's hologram distorter to disguise herself and leaves Gotham once again.
Years later the Phantasm worked as an assassin for hire, and was employed by Amanda Waller to kill the parents of Terry McGinnis, whom Waller wanted to transform into a new Batman. However, just as Andrea was about to deliver the killing blow, she hesitated, realizing murdering the McGinnises would be against everything Batman had stood for. This left Terry's family intact, however he eventually did become the second Batman after the murder of his father.
Andrea was skilled in martial arts having studied since her teens, but most of her abilities stemmed from her costume. She wore a protective bodysuit that offered some limited protection from impacts, and utilized a blade on one hand and a special gauntlet that emitted smoke.