Externals

The Externals are a group of fictional characters appearing in American comic books published by Marvel Comics. Considered a rare subspecies of mutants, most of them were X-Men antagonists. The original, unused name for the group was to be The Prophets, as seen on the back of the Sunspot & Gideon trading card included with X-Force #1. The characters first appeared in X-Force #10.

Background

The Externals are all mutants with the additional gift of immortality and, as expressed by Cable, they play an important role in Apocalypse's rise to power at least in one future. Their true origins are scattered throughout history, but it is known that they all share a psychic link with each other that separates them from other immortals. This psychic connection allows them to not only sense each other and their whereabouts, but allows them to summon each other at will from great distances. They also can sense when one rises from the dead and when one is killed. Saul, Absalom, Gideon, Nicodemus, Burke, Selene, Candra, 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 did not take any part in 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, after he was killed by Sauron. His revival was sensed by the other Externals, who declared that he represented hope. Later, Selene betrayed her fellow Externals and despite the efforts of X-Force, she managed to kill 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, later Cannonball was shot three times through the chest by the Purifiers, and was back up and around in a matter of hours. When asked about it, Beast mentioned Cannonball's status as an immortal again, though it is not sure if he was joking or not. Originally, Apocalypse was not considered to be External, though sometimes referred to as one. 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. Selene herself needs to maintain her supply of life force that she drains from human victims.
However, it was revealed that all Externals previously believed to have been killed by Selene or the Legacy Virus had in fact survived. The only way of effectively killing an External is by destroying their hearts, which consequently channels the life-force of the dead External into others, making them virtually all-powerful. Selene reveals she did not accomplish this deed herself because she could not handle the accompanying stress. Selene's assumptions about Cannonball and Apocalypse's status as Externals also cannot be taken as fact, as she incorrectly describes a total of seven Externals, rather than eight. Evidently, as long as there are at least two living Externals in a single timeframe, those who have died will be resurrected. This was the case with Burke, who was killed by the future version of Gideon, only to be reborn as a baby because the present versions of Selene and Gideon were alive. It is later confirmed that Apocalypse is an External and participated in the creation of Candra's gem with Selene and the other High lords eons ago.
Following the creation of a mutant nation on Krakoa, Apocalypse rescued his first Horsemen. He summoned his fellow Externals to the Eternal Caldera on Krakoa, revealing his intentions to sacrifice some of their life energy to power the Arak Maw Gate. Selene, Gideon, and Absolom are revealed to be a part of his plan and quickly turn on their fellow immortals. With the unexpected help of Rictor, the group wipe out four of the Externals and extract their life energy to fuel the gateway to Arakko.
It was later believed the mutant White Sword was an External, when Summoner described him as "immortal" and "External" to his grandfather Apocalypse. White Sword is later revealed to not possess immortality. However, similar to the Externals, he can be permanently killed if he is stabbed in the heart.

Other versions

Askani World

On Earth-4935, the Externals were purged by Apocalypse, who ascended to power and took control of the planet up until the 39th century.

Age of Apocalypse

In the "Age of Apocalypse" storyline, Candra, Selene, and Gideon appear as members of the Horsemen of Apocalypse.

In other media

Saul and Gideon make a non-speaking cameo appearance in the X-Men: The Animated Series episode "Sanctuary".