The origins of the Hellfire League of Injustice are shrouded in mystery, due to their only true appearance being at the beginning of JLX Unleashed #1. It is known that Firebird joined the team of supervillains at the end of the Armageddon Agenda storyline, in which Hellfire League member Maxwell Hodge released her Dark Firebird persona from inside her. The new villain joined with the Hellfire League of Injustice.
Curiously enough, the Hellfire League of Injustice seemed to be an anti-metamutant group, even though two of their members (Dark Firebird and Mistress Maxima) were metamutants. The group's most infamous action was the summoning of the demon known as Fin Fang Flame, who they summoned to destroy all metamutants. Fin Fang Flame started by destroying all four of the Hellfire League, before moving on to attack the Judgment League Avengers and JLX.
Though the entire Hellfire League of Injustice was presumed dead after Fin Fang Flame attacked, they may not have been truly killed after all. The 'true fate' of the Hellfire League was discovered in JLX Unleashed #2, though no more information was released on what this 'true fate' was.
The clear leader of the Hellfire League was Savage Shaw , who may have been worshipping or working with a powerful demon known only as Mephiston, who gave him the power to summon Fin Fang Flame. Savage Shaw also seemed to have a personal vendetta against the JLX specifically, from previous encounters with the heroic team. The Hellfire League's base was in a secluded shrine located somewhere in Senegal.