Agent X (Nijo Minamiyori, though chose the alias of Alex Hayden) is a fictional mercenary whose adventures have been published by Marvel Comics. He first appeared in Agent X #1 (Sept 2002), by Gail Simone and UDON.
The series, a pseudo-spin-off of Deadpool, continued the cynical, slapstick, and highly-polished action which had characterized its parent series. Indeed, a central feature of Agent X was the question of the title character's identity, sometimes implied to be Deadpool himself. Deadpool refers to Agent X as his "Earth-2 Counterpart", which might be a reference to DC's use of multiverses to explain multiple differences of the "same" character.
Agent X replaced Deadpool with a similar protagonist, while including ambiguous hints as to the nature of his relationship with the original character. Agent X was well-received by critics but wasn't a sales success. Some felt this title suffered due to Marvel's lack of support for both this and Soldier X as neither title enjoyed house or trade support. Simone publicly clashed with Marvel's editorial staff as the relaunched title struggled to find a foothold. Simone left the book after issue 7, with the protagonist's true identity still unrevealed.
The book's sales further suffered, prompting Marvel to cancel the book. The company then changed course to publish a series of fill-ins, to mixed reviews. Towards the end, two of these fill-ins were published to small fanfare: those by noted author Evan Dorkin and the acclaimed art team of Juan Bobillo & Marcelo Sosa. Soon after, Agent X was canceled with issue #12. However, shortly after this announcement, Marvel decided to launch a Cable & Deadpool book as a change in direction, which ended up being a much more successful consolidation of the two characters into one title. This allowed Simone and UDON to complete their initial vision as part of a three-issue arc tying up the loose ends and restoring Deadpool for use in the new book, which was published after a month's hiatus as Agent X #13-15.
Agent X also appeared in Cable and Deadpool #11-12. He would make another appearance in #38-39, where he was captured on a mission against HYDRA, who were able to give him arthritis using new technology, then morbid obesity so he wouldn't notice the arthritis. He was subsequently rescued by Deadpool, who was hired by Sandi and Outlaw. After being rescued, Agent X decided to allow Deadpool to run Agency X until he was cured of his disabilities.
In the 'Dear Deadpool' section of #37 the writers jokingly hinted that Agent X may receive a new ongoing series sometime in the future.
However, Alex Hayden soon emerged in New York with one goal in mind - to be the best mercenary alive. He was found by Sandi Brandenberg, Deadpool's former secretary, who assumed he was Deadpool by his powers and demeanour. He subconsciously took the name as a combination of composers he liked: Alexander Grieg and Josef Haydn, which Sandi worked out through his fondness for classical music. Sandi's friend and distant romantic interest Taskmaster was sought to help him get his bearings and train him, as was Outlaw, for her shooting skills. Taskmaster noticed Alex was ambidextrous and that he was somehow interfering with his reflex ability while training with him. Taskmaster then knew he couldn't be Deadpool, despite his healing factor and recognition of him and Sandi, and Outlaw corroborated this as Alex proved to be a better gun talent than Deadpool. Sandi and Alex formed a mercenary group, Agency X. The headquarters is based out of an amusement park Alex acquired as payment for his first mission.
Alex ran into Outlaw while assigned to try and take out the Punisher and steal his Colt .45 handguns. They failed and were locked up in a phone booth minus their weapons and clothes by Castle. The Punisher then killed the people who had sent them. Afterwards, Outlaw and Alex became romantically involved. However, Taskmaster, who was jealous of Sandi's attachment to Alex, had set up Alex on that mission and he was kicked out of the agency. He then contacted Higashi, the new leader of part of the Four Winds organization and informed them that Alex was Deadpool, who still held the credit for killing the previous four crime heads. The organisation, primarily directed by Higashi's enforcer, Saguri, therefore held Alex, Sandi and Taskmaster responsible but with Outlaw's help, the three made a last stand at the amusement park against an army of mercenaries and supervillains, while Sandi was given to Higashi to safekeeping, as his infatuation with her would keep her protected. Agency X were triumphant and Alex blackmailed the crime lords into submission, while killing Saguri after surreptitioiusly being hired by Higashi to do so. Higashi was also convinced by Sandi that Alex was not Wade Wilson and was now more fully in control of his group, so he agreed to prevent any further reprisals on the foursome. Alex was enthused at what appeared to be a fresh start for the Agency but was hurt when Outlaw announced her desire to return home to the South to care for her dying father instead, while Taskmaster declined a full-time position.
Alex performed his assignments solo from then on, but he found his personal life further muddied when he and Sandi spent a night together. He became disillusioned with his work and decided to shut down the agency, but found himself unable to tell Sandi, who by then had set up a job for he and Taskmaster to act as bodyguards to Higashi as a final act of ceasefire. While on their way to a meeting between the Four Winds families, Alex's group was attacked by a pair of over-cheerful assassins, but after a frantic battle, they arrived safely to find one of the Four Winds families had ordered the hit on Higashi. Now that Higashi was indebted to them, Alex, Taskmaster and Sandi returned to Sandi's apartment to find Black Swan and a tabula rasa Deadpool waiting. It turned out that all three had partially merged during the explosion when Black Swan used his powers in an act of desperation to save himself. Black Swan psionically acquired Deadpool's healing factor but accidentally made contact with Nijo and personal traits had been mixed around. Swan had given also Nijo's corpse Deadpool's regenerative powers (restoring him to a form of life 5 minutes after his death), as well as part of his personality, while Nijo also gained Swan's firearms talents, ambition, some of his refined tastes, preferences and intolerances and also the bodily scarring and outrage he'd received from Deadpool throwing him face first into a white hot fireplace griddle at his home.
Black Swan proposed a three-way mind meld to restore each man to their correct personal states, but doublecrossed them. Outlaw returned in time to help fight the Black Swan, who had now absorbed both Alex and Deadpool's powers to augment himself. Even though Alex called Higashi's favour in and surrounded Swan with hitmen, this proved to be fruitless, so Alex devised a new plan. After Taskmaster and Outlaw distracted him, Deadpool pinned Swan to Taskmaster's explosives-laden van and Alex ignited it. Alex then reversed Black Swan's absorption, but also gave him the memories of being caught in the bomb explosion in Germany. The group then repeatedly shot the Black Swan to make sure he was dead. The body was taxidermied and carried around by each couple (Taskmaster and Sandi, Alex and Inez) as a prop while they went on vacation.
When they later found themselves on opposing sides over the fate of Cable, Alex had another confrontation with Deadpool, which he lost initially, giving Deadpool the opportunity to spell out "Hi, Weasel" with his entrails as a "surprise" for his best friend. Unable to do much damage to each other due to their healing factors, they relented after Wade agreed to hand Alex his pancreas back.
After a botched attempt to steal a device from Hydra, Sandi and Outlaw convinced Deadpool to rescue Alex. Alex had been affected by the device he was supposed to steal, giving him arthritis and "the American gene" (which resulted in making him incredibly fat). This made escape physically impossible - though he wouldn't want to miss out on the many treats and monkey chow that were being given to him as a lab specimen. Deadpool managed to free Alex with the help of Bob, Agent of HYDRA. He then asked Deadpool to run Agency X whilst he got himself back in shape, reasoning with himself that his only other alternatives were to shoot himself or eat Sandi and his business.