Jamie Madrox is born to a family living near the Los Alamos research facility in New Mexico; the background radiation may have stimulated his mutation. When Jamie is born, the doctor's slap causes him to multiply into two identical babies, which shocks his parents and the doctor. Professor Charles Xavier, a friend of the Madrox family, suggests that they move to Kansas to raise the boy in privacy. Dr. Daniel Madrox, Jamie's father, creates a suit for him to wear which is designed to absorb kinetic energy, the source of the duplication. Later, Damian Tryp, of Singularity Investigations, makes his own offer to look after Jamie, claiming that Jamie is not a mutant, but a "changeling", a predecessor to mutants who develops its powers at birth. Jamie's parents refuse to give Jamie to Tryp. At fifteen years old, Madrox's parents are killed by a tornado alleged to have been caused by Tryp and he begins to run the farm by himself along with his duplicates, or "dupes", until his suit is damaged.
Madrox goes to New York City for help, where he meets Mister Fantastic of the Fantastic Four. He contacts Professor Xavier, who sends the youth to Muir Island with Moira MacTaggert, working as a laboratory assistant to help her with research. He later helps Moira and fellow mutants Havok and Polaris in searching for the escaped mutant, Proteus. One of his duplicates is consumed as a host body for Proteus, though Jamie remains fine. Following the X-Men's battle with Proteus on Muir Island, Madrox was invited to join the X-Men, but he declined. One of Jamie's renegade duplicates later searches with Siryn for the runaway New Mutants Sunspot and Warlock. They find him and Jamie joins the Fallen Angels.
Jamie is then one of the residents of Muir Island who comes under the mental control of the Shadow King. Following the destruction of Muir Island and the defeat of the Shadow King, he becomes a government operative as a member of the second X-Factor team, which is assembled by Val Cooper. Here, he to develops a reputation as a prankster, forming a friendship with teammate Strong Guy. Also on the team is former New Mutant Wolfsbane, who later joins his X-Factor Investigations. In the first day of the team, one of his duplicates is shot and killed, and Madrox learns for the first time that he cannot absorb a deceased duplicate. This makes him realize for the first time how independent his duplicates actually are. This becomes clearer to him when a duplicate, working for Mister Sinister, decides that it wants to absorb the original, which it does for a short time, until Jamie's dominant personality broke free and reabsorbs the wayward dupe. After he is exposed to the Legacy Virus while performing CPR on an infected Genoshan mutate, Jamie is forced to kill the Acolyte Mellencamp in self defense by creating a dupe inside the mutant while his hand is in Mellencamp's mouth. Madrox does not often fight in cosmic battles like most of the other X-Men, but he fought doppelgangers during the Infinity War and, along with Wolfsbane, as the two are religious, are taken by the cosmic entity Goddess during the Infinity Crusade. Jamie's health continues to deteriorate due to the Legacy Virus. An attempted cure by Haven leaves him dead until it is revealed that it was a duplicate who had been infected and died; the real Madrox was alive and suffering from amnesia. Jamie is the motivation for the Government-sponsored version of X-Factor to break ties with the government and go underground when the team is tricked into thinking Jamie and his duplicates are actually a squad of super-powered terrorists. Eventually, the team discovers this was a manipulation and the group goes rogue, splitting from the government. He seeks out Strong Guy, who is ill after Jamie's alleged death. Unfortunately, this makes Strong Guy even weaker, but Jamie's mistake is fixed by the genius of new team leader Forge. He the serves as majority staff for Banshee's X-Corps. Banshee hired ex-criminals to police other mutants but things get bad when Mystique goes on a murderous rampage and has Mastermind's daughter mind control them. The X-Men manage to defeat the renegade X-Corps members, he transfers to one of Xavier's official "non X-Men" mutant teams in Paris' X-Corporation, fighting Weapon XI in the Channel which results in the death of teammate Darkstar.
After the fall of the X-Corporation, Madrox begins working as a private detective in the "Mutant Town" area of New York, along with former X-Factor teammates Wolfsbane and Strong Guy. In the passing time, Madrox has been sending out his duplicates to lead lives of their own. Among these dupes are a Shaolin monk and an Olympic Gymnast. By this point, his powers are developed to such an extent that any dupe who gains sufficient skills can pass its' knowledge on to Jamie, giving him a wide variety of training instantly. The side effect of excessive withdrawal from absorbing the duplicates leads him to gain their new personalities as well, which gives him a form of multiple personality disorder, in which any new dupes may spontaneously generate any individual personality aspect of Jamie Prime, making them unpredicatable, as they more often than not disobey his orders or manifest as personalities that are too volatile or meek. It is during this period that he encounters an assassin named "Clay", who has the same powers as Jamie. While killed after telling Jamie that the Multiple Man has no idea what he truly is, Clay would come back later.
After "House of M"'s elimination of mutants, it is revealed that Jamie has upgraded his private detective agency to a new building, under the name X-Factor Investigations. He bought the building using money from a Who Wants to Be a Millionaire-type show, using a room full of dupes as a lifelines. Still suffering from uncontrollable duplicate personalities, Jamie sends one to talk a de-powered Rictor out of jumping off a building and instead pushes him off. The dupe calls himself "The X-Factor" and threatens Madrox that he will come out whenever dupes are made, and Madrox won't be able to tell before being reabsorbed, and Jamie's new team adds Rictor to the group, along with M, and Siryn. Celebrating a victory after discovering he's not a mutant, but a changeling, Jamie has sex with Siryn, and an accidentally forgotten duplicate with M. When Jamie discovers and absorbs the duplicate, both females are furious with him. Later, Layla Miller, who is without a home after House of M's reality is shattered, reveals to Jamie that one day they will get married, and Wolfsbane will kill them both on their wedding night. During "Civil War", a duplicate of Jamie had created a few years ago eventually becomes agent of S.H.I.E.L.D., who registers M and Rictor since he is an enforcer of the Superhuman Registration Act, he registered M and Rictor. However, the true Jamie and X-Factor stand opposed to the legislation, going so far as to make a public statement regarding their position, leading Jamie to go in direct opposition to the neutral stance taken by X-Men leader Cyclops, who Jamie is upset at for his withholding the truth about M-Day. Jamie also declares that the empty Mutant Town will be a sanctuary for superheroes being pursued by the government. Agent Madrox recently met "his" end when he was surprised and re-absorbed by the original Madrox during an investigation of a HYDRA cell. Jamie Madrox continues the task of hunting down his stray duplicates and reabsorbing them, but he leaves one, John Madrox, who has carved out a life for himself as an Episcopal priest, husband and father, and Jamie decided not to reabsorb him. Siryn also discovers that she is pregnant by Jamie.
During the "Messiah Complex", Cyclops sends Jamie and Layla to go see Forge, who has built a machine that allows him to monitor alternate timelines. Madrox sends two dupes to find information on two timelines that showed "spikes", after the birth of the Mutant baby, due to two different timelines: one in which the newborn becomes the planet's savior and another where it becomes its dominator. Before anyone can react, Layla jumps into the portal along with one of the dupes, and Madrox collapses into a coma. Layla and one Madrox duplicate arrive eighty years in the negative future to discover that the mutant race has been severely decimated. Mutants are imprisoned in concentration camps overseen by humans. Layla and the dupe are captured and tattooed with an "M" for mutant over their eyes. There, they encounter a youthful Lucas Bishop, who said that he would gladly go back in time to kill the mutant baby responsible for the way this timeline has turned out. Layla straps a stolen grenade to the duplicate, killing him and sending his memories of the event back to Jamie so he can tell of Bishop's treachery. When Jamie awakens, he develops an M tattoo because his body takes on scarring from duplicates. Jamie leaves and returns to X-Factor Investigations, disillusioned due to Layla's loss.
Siryn goes into labor and proposes to Jamie, who accepts. She gives birth to a boy, and they name him Sean, after her father. Just hours after his birth, however, Sean, much to the horror of Jamie, Theresa and X-Factor, is absorbed into Jamie's body as Jamie holds him, completely against Jamie's will. Jamie realizes that the baby must have been fathered by a dupe rather than him, and that "the offspring of a dupe isn't really anything more than a dupe". Siryn, filled with rage toward Jamie, breaks his finger and tells him to leave. Jamie goes to see his preacher dupe John Maddox. Jamie realises that if the child of a dupe is merely an "infant dupe", then John's son should have been absorbed either by John himself, or when Jamie ruffled the boys hair; therefore John's son must not be his. John admits that he already knows his wife had an affair. Jamie then reveals that he plans to kill himself over the grief caused by Sean, but is prevented by a holographic projection of an adult Layla Miller, who takes him into the future.
Jamie is transported to the future in the midst of the Summers Rebellion, where mutants rise up against Sentinel and human oppressors, which is led by Ruby Summers, the daughter of Cyclops and Emma Frost with her fathers' eye beams and Emma's organic mineral body, Layla, and a cyborg Cyclops, whose predicament is Jamie's fault. After kissing Layla (now an adult) out of happiness at seeing her, Cyclops wants Jamie to find out why some mutants are winking out off existence. The group visit an aging senile Doctor Doom, who says Layla told him in the past that he'd have to instruct Jamie and her on something in the future, and it is now. In the present, X-Factor and new members Longshot and Darwin are battling Cortex, an agent of the Summers Rebellion era government. Cortex briefly controls Shatterstar and M, using them to respectively make assassination attempts on Reverend John Maddox and an X-Factor client. Cortex grabs Longshot, trying to also control him, and realizes him and Shatterstar are connected, and when Cortex loses control over Monet, she attacks him and his hood falls back revealing that he is the second Jamie Madrox duplicate from Messiah Complex.
Powers and Abilities
Kinetic Duplication: Madrox creates identical duplicates ("dupes") of himself and all items on his person through the absorption of kinetic energy, whether through collisions, being punched, snapping his fingers, etc. Each dupe has the same powers and abilities as the original Madrox and is capable of independent thought. The original Madrox and dupes are telepathically and empathically linked. Madrox originally was limited to creating around 40 duplicates, but has since demonstrated the ability to create numbers far beyond the original limit. A created dupe tends to manifest a particular aspect of the original's personality; lengthy separation without absorption (see below) has been shown to increase this manifestation and increase the dupe's independent will. Prolonged separation has occasionally resulted in the dupe attempting to maintain his separation from the original and resist reabsorption, sometimes by force.
Duplication Absorption: The original Madrox can absorb them back into himself at will, at the same time absorbing the memories, skills and experiences of the duplicate.
- Duplication Experience Transference: Madrox merges back, he retains memories (albeit somewhat imperfect), knowledge, and experiences of the dupe.
- Duplication Healing: He also uses merging as a form of healing - Originally, uninjured dupes "shared" the damage when they reemerged (e.g., if an injured dupe merged with an uninjured Madrox, the resulting Madrox had an injury half as severe as the original injury). Now, however, the core Madrox can reabsorb injured or even near-dead dupes without taking on any of their physical injuries at all.
Madrox has acquired extensive knowledge and skills via his duplicates' experiences, such as human anatomy, speaking Russian, and Shaolin monk stealth techniques. He also has hand-to-hand combat training, learned as part of X-Factor and from a dupe who studied martial arts. Madrox is a certified lawyer, has medical training, and training as a gymnast, and can pick locks.
Jamie Madrox possesses the normal human strength of a man of his age, height, and build who engages in intensive regular exercise.
Madrox used to wear a suit that damped kinetic impacts so that he wouldn't duplicate from accident impacts.