When a top-secret program attempted to recreate the original Weapon X experiment that involved the feral mutant Wolverine, they failed to secure a test subject that could survive the bonding of the virtually unbreakable metal Adamantium to their skeleton. Seeking to take the project in a new direction, the project's director, Doctor Martin Sutter, recruited renowned mutant geneticist Doctor Sarah Kinney and tasked her with creating a clone. Using the only available genetic sample from Weapon X, which was damaged, they were unable to salvage the Y chromosome after 22 attempts. Kinney then proposed they create a female clone, and though her request was initially denied, she still went ahead and produced a viable female subject, prompting Sutter to reconsider. Despite resistance from his protégé Doctor Zander Rice, whom he had raised after Rice's father was killed by a bestial Wolverine at the original Weapon X Project, Sutter allowed Kinney to proceed. As revenge for her insubordination, Rice forced Kinney to act as the surrogate mother for the clone, and she gave birth to "X-23."
Raised in captivity, X-23 was trained to be a weapon. Kinney did her best to ensure the child retained some semblance of humanity, but her efforts appeared to be in vain. After seven years, Rice had X-23 subjected to radiation poisoning in order to accelerate the activation of her mutant gene, then forcibly extracted her claws and coated them with Adamantium. Next, Rice created a chemical compound he called "trigger scent" that sent X-23 into an involuntary berserker rage upon smelling its presence. Three years later, X-23 was sent on her first field mission to kill Presidential candidate Greg Johnson. Numerous other missions followed, as X-23's services were sold to the highest bidder, and she was left emotionally stunted as a result. Rice, in an attempt to avenge his father's murder, abandoned X-23 on a particularly dangerous mission, but she survived against overwhelming odds and managed to return to the facility.
Ultimately, Rice persuaded Sutter to hand over control of the program to him, then secretly ordered X-23 to kill Sutter and his family. Later, Rice revealed to Kinney a chamber with dozens of incubation pods containing female clones before he fired her. Before fleeing the facility with X-23, Kinney gave her one last mission - destroy the pods and kill Rice. However, Rice was able to exact revenge on Kinney from beyond the grave, as he had earlier exposed her to the trigger scent, sending X-23 into a rage that caused her to kill her mother. As she lay dying, Kinney named X-23 Laura.
X-23 surfaced in New York two years later and was found living on the streets by a pimp named Zebra Daddy, who took her in and employed her as a prostitute. During her time as a prostitute, X-23 seemed to suffer from a self-mutilating disorder. She superficially cut herself with her own claws whenever she was in a threatening situation. She also seemed to suffer some personality issues which left her mostly mute and unable to free herself from the grip of Zebra Daddy. X-23 started to come to her senses after she met Kiden Nixon, a young mutant with the ability to freeze time when in danger, and together with Kiden's teacher, they rescued another young mutant, the feral Catiana, from an angry mob. Zebra Daddy tracked X-23 down, but with the aid of her newfound friends and the mutant named Felon, Zebra Daddy's thugs were defeated. X-23 then killed him to save the lives of her friends. X-23 later took a job at the mutant-themed Wannabee's nightclub in the Mutant Town district of New York. It was there that she saved the life of the daughter of mob boss Don Parisi from a gang of thugs, whom she killed. The deaths inadvertently implicated Wolverine, prompting his teammates in the X-Men to investigate. X-23 instinctually attacked Wolverine on sight, but he was eventually able to calm her down, and she led the X-Men to Parisi's daughter. After aiding the X-Men against Parisi's super-strong mutant enforcer Geech, X-23 fled the scene. She later returned to help the X-Men save victims of a car accident, after which she was enrolled at the X-Men's Xavier Institute.
X-23 quickly became very protective of Wolverine, attacking his teammate Bishop after he felled Wolverine during a training session. She also took to observing Wolverine on the mansion's security monitors. During one such viewing, an anomalous energy spike prompted X-23 to investigate. Encountering Spider-Man at the source of the signal, X-23 initially mistook him for an enemy and attacked. The pair ultimately teamed up to save the young mutant Paul Patterson from an alternate reality version of the armored Avenger Iron Man. The arrival of the heroic Captain America and the super-spy Black Widow helped turn the tide. X-23 then secretly followed Wolverine on his investigation of strange activity in the Canadian Rockies. Ambushed by the Hauk'ka, evolved Saurians from the Savage Land, X-23 managed to escape and alert the X-Men. Traveling to the Savage Land, X-23 and the X-Men teamed with the Land's lord Ka-Zar and his circumstantial allies, the Savage Land Mutates, to prevent the Hauk'ka from destroying human civilization by controlling the weather-manipulating X-Man Storm.
Sometime later, X-23 turned up in the in two other X-titles, without her friends. She was accused of the murders of four humans that were investigated by Wolverine and his fellow X-Men. (While she was responsible for the murders, she committed them because the victims were brutally attacking a young woman.) After a brief conflict with the mutant heroes, X-23 came to live with them at the Xavier Institute. She has nearly no social skills, so Wolverine is helping her adjust to her new life. She seems to be making friends with Shadowcat, Psylocke, and Rachel Summers. X-23 was approached by the cosmic Uni-Power in hopes of making specific use of her healing ability. Although she initially resisted its attempts to bond with her, and she remained reluctant even though it pleaded with her, she ultimately agreed to aid it and became Captain Universe for a brief time.
After the effects of House of M|"M-Day", X-23 was one of the few students who didn't lose their powers. The depowered students and staff were sent home; however their bus was bombed by anti-mutant religious zealot Reverend William Stryker. Subsequently, Emma Frost had the surviving students engage in an all-in brawl, with those deemed to be the best performers assigned to a new team of trainee X-Men. Despite Frost's attempts to omit her, X-23 was among those students who made the grade.
Shortly afterwards, following Stryker's attack on the ex-mutant students, X-23 heard Dust talking to Icarus, who had fled the Mansion. Dust intended to meet Jay, but Laura told her it was a trap, and had to knock out her roommate to keep her safe. Donning Dust's burkha X-23 came to Stryker's compound and was shot. After a few minutes spent healing and playing possum, Laura returned to the Mansion to help fend off Stryker and his goons.
The team gave more respect to Laura following her part in stopping Stryker's attack, in which she single-handedly killed three Purifiers. Following that she started to bond with her friends, using her enhanced hearing to find out what happened to Icarus for them, learning that Stryker killed him.
After Surge received a distress call from Forge, X-23 followed the team along to Dallas to rescue him from the Sentinel Nimrod. At the height of the desperate battle she managed to cut through to the interior of the machine with her claws, allowing the Sentinel to be defeated. She was wounded during the battle and was unable to heal herself. In order to save X-23, Julian supercharged his telekinetic powers with the help of Emma Frost in order to rush her back to the mansion where she was healed by Elixir. As Hellion recovered his strength, and found that his power levels were enhanced, Laura kept watch over him. Emma Frost confronted Laura, asking her to leave the school because of the trigger scent saying that she was a danger to everyone at the institute even Julian. Their conversation is cut short by Cessily (Mercury) coming to Laura's defense. Mercury persuades Laura to go for coffee and discuss Laura's crush on Julian. However, the cafe is attacked by Kimura and her minions. though Laura thought that Kimura was after her, she was really after Cessily.
Laura goes back to the Xavier Institute when Hellion interrupts her as she is gearing up to attack against the facility. He informs her that he is coming with her. The two find a hide out where Laura interrogates a man at gun point. Upon securing the information she needs, X-23 shoots him in the head. Julian is shocked and tells her that killing will no longer be a part of their interrogation technique, X-23 remains silent and the two continue their search for the facility.