The Externals are all mutants with the additional gift of immortality and, as expressed by Cable, they play an important role in the future and Apocalypse's rise to power. Saul, Absalom, Gideon, Nicodemus, Burke, and Crule formed the self-fashioned "High Lords", bent on playing power games and manipulating events behind the scenes. Crule was employed as an enforcer and assassin for the other High Lords, while Candra and Selene preferred to play their own schemes separately and didn't take any part on the High Lords gatherings. Each External was claimed to represent an intangible concept:
At one point, X-Men regular and former New Mutant Cannonball was declared an External by Cable. Later, Selene betrayed her fellow Externals and despite the efforts of X-Force, she managed to slay them by absorbing their life forces. Selene ultimately escaped, but not before summarily dismissing the assumption that Cannonball was an External, calling into question Cable's conclusion and the reasons for it. Yet, more recently, Cannonball was shot three times through the chest by Reverend Stryker'sPurifiers, and was back up and around in a matter of hours. When asked about it, Hank McCoy mentioned Cannonball’s status as an immortal again, though it’s not sure if he was joking or not. Apocalypse has also been referred to as an External on several occasions; his longevity is believed by Selene to be mostly due to technological means, although Apocalypse was already many centuries old before his first encounter with the technology he would later integrate himself with. To note, Selene herself needs to maintain her supply of life force that she drains from human victims. More recently however it was revealed that all Externals previously believed to have been killed by Selene or the Legacy Virus had in fact survived. As it turns out, apparently the only way of killing an External is by removing their hearts and only an External can kill an External. When one of these immortals kills each other, their power and life-force is channeled into them making them virtually all powerful. Selene reveals she didn't accomplishing this deed herself because she could not handle the stress that came with it. Also, Selene's assumptions about Cannonball and Apocalypse not being part of the Externals cannot be taken lightly as she mentions to be a total of seven Externals when there's actually eight. Evidently, even after death, as long as there are at least two Externals alive, those who died will simply be revived in a new form, as was the case seen with Burke, who was killed by the future version of Gideon only to be reborn as a baby with purple eyes because the present versions of Selene and Gideon were alive.
Other versions
Askani
In, the Externals were purged by Apocalypse who ascended to power and gained control of the entire planet up until the 39th century.
Age of Apocalypse
In the alternate reality created when the time traveling Legion killed his own father, it's unknown what happened with the Externals as only a few had made their presence known as soldiers of Apocalypse. Candra, Selene and Gideon were recruited as the first wave of Horsemen of Apocalypse.
In other media
''X-Men: The Animated Series''
In the episode "Sanctuary Part 2", Saul and Gideon are seen watching Fabian Cortez announce his scheme to the Earth.
In the episode "Externally Yours", Gambit's past involvement with the respective guilds of Thieves and Assassins, as well as with the External Candra are detailed.
