The JLX are the Amalgam of Marvel Comics' X-Men and DC Comics Justice League International, and made their first true debut in JLX #1, though in the Amalgam Universe, their first appearance was in the fictional JLA Annual #13.
The beginnings of the JLX started with JLA #122, when the Mariner was framed by Will Magnus for the destruction of some Roxxon oil tankers. The Mariner went on the run, and S.H.I.E.L.D. and the Judgement League Avengers went after him. However, most of the metamutants in the JLA believed that the Mariner was innocent. They were contacted by the mysterious Mister X, who had once funded the JLA, until the JLA discovered that he had a criminal record. For unknown reasons, Dark Claw was the only metamutant on the team not contacted by Mister X.
Mister X assembled Apollo, Firebird, Nightcreeper, Mercury, Wraith, and Runaway. Together the team became known as JLX, and freed the Mariner from where the JLA had locked him away. The Mariner joined the team. After the JLX had freed the Mariner, the JLA went after them. In an epic battle shown in JLX #1, the entire JLA fought against the JLX. The battle stopped after Mister X contacted Angelhawk, informing him to fake an injury, which he did. In turn, Mister X kept Angelhawk's metamutant origins a secret.
The JLX fled to their submarine, the Wavecruiser. Mister X and the Mariner had apparently been doing some mental probing, so that the Mariner could find once more his lost city of Atlantis. When the JLX finally discovered it, it was abandoned, other than the presence of the mutant-hating Will Magnus, Jocasta, and Magnus' Sentinel, giant mutant-hunting robots. After Wraith destroyed Jocasta, they realized they would not be able to defeat the Sentinels. To everyone's surprise, Mister X revealed his true form, the form of a Skrull named J'onn J'onzz. He singlehandely destroyed the Sentinels, and revealed his true origins to the JLX.
The original JLX series only lasted for twelve issues. In the course of the series, the team met up with new mutants, including Kokoro, Sunstorm, and Wondercat. An old friend from the JLA joined them as well, Angelhawk finally revealing his metamutant status to the world. During the story called the Dark Firebird Contract, Firebird's Dark Firebird persona was released by Mister Mastermind. Mister X and Niles Cable of the X-Patrol joined forces to pull the Dark Firebird persona back inside her, with great risk to themselves.
In an important story called the Armageddon Agenda, the JLX finally found the true Atlantis. However, the Mariner's reunion with his people short, Will Magnus and his Sentinels were given permission by the government for a fullscale attack against metamutantkind. Half of the population of Atlantis was wiped out, resulting in the Mariner being banished from Atlantis. Mercury returned to the future with the help of Iriskani and Wraith disappeared with the assistance of the Shadow Guild. Firebird was captured by Maxwell Hodge, who released the Dark Firebird persona inside of her once again. The rest of the JLX were captured after the battle, which resulted in Mister X being confined to a wheelchair, Angelhawk having his wings removed by force, and Apollo left in a catatonic state.
Meanwhile, Maxwell Hodge and Dark Firebird had joined forces with Savage Shaw and Mistress Maxima to form the Hellfire League of Injustice. This group summoned Fin Fang Flame in the JLX's second series' first issue, JLX Unleashed #1, a giant, fiery dragon, who they commanded to destroy all metamutants. Fin Fang Flame rebelled against them and (supposedly) killed all of them instead, moving on to attack the Judgment League Avengers. After destroying the JLA West and JLA International teams, he moved on to the main JLA team, where Super-Soldier was struck down, and Amazon faced off against him. Fin Fang Flame informed Amazon that he planned to destroy all metamutants, and any beings in his way. Amazon managed to escape to where the JLX were being held.
Amazon freed the remaining JLX and joined the team, the team now consisting of Mister X, Apollo, his brother Chaos, Nightcreeper, Runaway, Iceberg, and Amazon. The JLX went into battle against Fin Fang Flame, and after a long and destructive battle, Fin Fang Flame was eventually defeated, after Apollo absorbed the energy of Fin Fang Flame, causing a second mutation. With this came the official return of the JLX as a team.
As the JLX made their way from metamutant menaces to some of the greatest Amalgam heroes on the planet, they made numerous enemies along the way, including:
- Brotherhood of Injustice
- Dark Firebird
- Fin Fang Flame
- Hellfire League of Injustice
- Lord Nimrod
- Mister Mastermind
- Ms. Tique
- Will Magnus