Brood reproduce by implanting their eggs into other host species, allowing them to gain the skills of their host and even shape-shift into their host's form. The Firstborn have no host bodies however, and are instead hatched from eggs lain directly by the Brood Empress - the head matriarch of the Brood species. They religiously serve their Empress, declaring "There is no god but the Empress, and the Firstborn are her children!" The Firstborn are employed by the Empress only for situations of dire importance to her, such as if a Brood Queen were to go rogue. As the Empress' royal assassins, the Firstborn will kill their target without question, along with anyone that gets between them or even sees them attack their target, after which they kill themselves to leave no trace of their deeds. As they say, “We do not go back. We come, we kill, we die. That is all.”
The Firstborn were created by John Ostrander and Bryan Hitch. They first appeared in the 1996 two-part special X-Men vs The Brood.
Major Story Arcs
Day of Wrath
After Hannah Connover was infected by Josey Thomas with a Brood Queen egg, she used her husband William's traveling religious group to spread more Brood eggs to people. She gradually however was able to use her religious faith to get her human side back in control of herself, and she suppressed her Brood instincts.The Brood Empress saw this as a dire affront to her Brood will, and plagued Hannah with countless nightmares while sending her telepathic warnings. Jean Grey of the X-Men gradually managed to pick up on these telepathic warnings and alerted Professor Xavier to send the X-Men to help Hannah keep herself free of Brood control. With Hannah continually defiant to her will, the Brood Empress sent her Firstborn to kill the so-called "false queen."
Josey Thomas met up with the Firstborn after they arrived on Earth and directed them towards Hannah. Once Hannah was in sight however, the Firstborn killed Josey for her affiliation with Hannah, deeming her and all of Hannah's Brood "contaminated" in the eyes of their Empress. The Firstborn then advanced on Hannah, only for the people she'd turned into Broodlings to come to their queen to aid her. The Broodlings were no match for the elite Firstborn though and only the timely intervention of local authorities and the X-Men managed to save Hannah. Even the X-Men had trouble against the Firstborn, doing very little damage against the elite warriors, and only their combined might and the explosion of an oil tanker truck managed to kill just one of the Firstborn. The rest of the Firstborn retreated, having already successfully flushed out their prey.
The X-Men took Hannah with them to protect her, but Wolverine on the other hand insisted they kill Hannah for the clear Brood threat she represented. While the X-Men argued, the rest of Hannah's Broodlings came to defend their queen. Hannah called them off before a fight could erupt, but faced with the people she'd turned, she begged the X-Men to kill her for her sins. The X-Men refused to kill, period, and so Hannah had her Brood briefly fight the X-Men while she ran off to try and spare everyone from the threat of the Firstborn.
Hannah met up with the remainder of her Brood, only to be attacked by the Firstborn once again. Her Broodlings fought bravely but were viciously slaughtered by the Firstborn. The X-Men managed to arrive in a nick of time again to protect Hannah, ensuing in another fierce battle. Jean eventually sent Hannah away with Cannonball to save her, after which the Firstborn disappeared from the fight. They then managed to track down Hannah's husband William in order to use him as bait. Hannah sensed the Firstborn's intentions and turned into a full Brood Queen to save her husband. After a brief fight with the Firstborn, Hannah reverted back to her human self, horrified at what she had become. William told her she would be forgiven in the eyes of the Lord, but the Firstborn promised no such forgiveness and prepared to kill them both.
The X-Men however came once more just in time to save Hannah, and had come up with a plan, theorizing that if Iceman managed to cryogenically freeze her that her vitals would drop enough for the Brood to believe she was dead. Following Beast's instructions, Iceman managed to successfully freeze Hannah in a block of ice, causing the Firstborn to believe she'd perished when they could no longer sense her. Believing their mission to have succeeded, the Firstborn committed suicide for the glory of their Empress.
Although this group of Firstborn perished, as long as the Brood Empress lives, she will always be able to birth more of them.
Powers & Abilities
The Firstborn are very unlike standard Brood. They are large - larger even than most Queens - green, reptilian creatures covered in immensely durable armored bone plates, and possess claws made of this same bony material. Firstborn have no host bodies and therefore cannot shape-shift into any other form. They are fierce warriors - the X-Men have been shown to go through great efforts to take down just one of their kind - possess highly attuned senses, and like all Brood they possess a psychic link to their Brood matriarch - in their case the Brood Empress herself.
The Firstborn employ special ships that are presumably launched directly from the Brood's central nest world. These ships dissolve when the Firstborn arrive at their target, as they are never intended to return from their missions. They've also been shown to employ the ability to teleport on rare occasions, presumably achieved through technological means of some sort.