When Legion, the mentally unbalanced mutant son of Professor Charles Xavier and Gabrielle Haller, traveled back in time in an attempt to kill Magneto, he accidentally killed Xavier instead, creating a splinter universe known as the Age of Apocalypse. In that reality, mutants became the dominant species of the planet. Apocalypse rose to power and enslaved humanity.
When Apocalypse was making his rise to power, Christopher Summers and his wife took their boys Alex and Scott with them in an attempt to flee to Canada where it was supposedly safe. On the way, their ship was captured either by the Shi'ar or the Brood[1]. In a last-ditch effort to save their children, Christopher pushed both boys out of their plane with the only remaining parachute.
The two boys eventually ended up in a Nebraska orphanage run by Sinister, one of Apocalypse's Horsemen[2]. Sinister raised them like his own children, and they eventually became high ranking Prelates in Apocalypse's Elite Mutant Force. Alex would constantly live under his brothers shadow as Sinister was grooming Scott to be a born leader, creating a one-sided rivalry between the Summers brothers. Apocalypse eventually classified Alex as one of the "Forgotten", mutants that, in his mind, were deemed to be weak and therefore would have no future in his world where only the fit survive[3].
Both Alpha mutants, and both holding the rank of Prelate, Alex and Scott Summers dominated the new mutant aristocracy in Apocalypse's America. Sinister employed the brothers to operate his breeding pens, acting as security, and sometimes performing as a special ops unit. Scott's ability to show emotional restraint in battle earned him Sinister's favor over Alex, fueling a dangerous rivalry between the brothers. This rivalry worsened when the brothers reunited with their real father - Christopher Summers - but were forced to fight him when they discovered he had been infected with a Brood egg. While Alex was quick to accept their father's return, Scott would not be so trusting and ultimately, when the truth about Christopher's infection came to the fore, Scott killed Christopher, earning him Alex's eternal hatred[4]. At some point, Jean Grey became a prisoner of the Breeding Pens and become known to Alex, who noted his brother's fondness of her until she was rescued by Weapon X[5][6].
Alex continued his duties as one of the Elite Mutant Force. During this period, Alex spent his time frequenting Angel's bar, Heaven, where the elite would go to drink. There, he began an affair with Scarlett McKenzie, a human lounge singer who was also, unknown to Alex, secretly a spy for the Human High Council, this despite the fact that relationships between mutants and normal humans were against the law in Apocalypse's America.
Alex saved geneticist the Dark Beast from the Blob, an experiment that escaped and threatened him. Although Alex managed to fight the creature off, it would take Scott to kill him, further irking the younger brother[7].
Shortly after this, Apocalypse's outer sea-wall defense was breached by Jean Grey and Weapon X in an attempt to make an opening for a Sentinel evacuation of the remaining humans in North America. In answer to this security breech, Alex was transported to the weapons platform that Weapon X and Jean Grey were attacking. During the fight, the Sentinel the two mutant rebels used grasped Alex in one of its launch-able gauntlets, sending him through a transporter and fusing him with the gauntlet. This necessitated the Dark Beast to perform surgery to free Alex[8].
During this period, there were escapes of a number of mutants from the Breeding Pens, forcing the Elite Mutant Force to gather them up. When the escapee leader Artemis attempted to kill Scott, Alex stepped in and killed her. When Cyclops learned that Sinister had abandoned them, Havok began to believe that this was an opportunity to try and replace his brother as leader of the EMF[9].
When Scott and Alex reported Sinister's abandonment to Apocalypse, Scott earned Apocalypse's favor and was offered a position as a member of his Horsemen. Realizing his brother would not be interested in gaining power and being more dedicated to the pens, Alex became more determine to eliminate his brother. When investigating escapees from the Breeding Pens they investigated Lorna Dane, the only person to see who the mysterious person was that was breaking them out. Alex ultimately caught his brother Scott in the act of springing Lorna out of the pens, hoping to use it as a means of finally eliminating his hated brother[10].
Still harboring hostility against his brother, Alex re-captured the pen's former prisoner Jean Grey in order to use her against Scott. When Scott refused to execute Jean, Alex successfully exposed his brother as a traitor. The conflict escalated to a peak when Alex, with the help of Cannonball and Amazon, overthrew Cyclops as the head of both the Elite Mutant Force and the pens. Alex tuned Scott and Jean over to the Dark Beast for experimentation, however, they both managed to escape[11].
Meanwhile, Alex's secret lover, Scarlett McKenzie, was discovered to be an agent of the Human High Council. She was arrested by the Bedlam Brothers and taken to the Breeding Pens, where she was confronted by Havok and revealed to him that she was pregnant with his child. Before he could deal with her the power went out, and he realized that it was his brother escaping. He confronted Scott and Jean as they were attempting to break the slaves out of the breeding pens. During the fight, Alex was knocked out and Scott couldn't bring himself to kill his own brother and so he and Jean left[12].
During the final battle at Apocalypse's citadel, Alex tracked down Jean and Scott. Havok used his powers to slay Jean Grey, who was using her powers to keep the nuclear bombs launched by the Human High Council at bay, dooming them all. When confronted by Scott, Alex used his powers in an attempt to slay Scott as well. Alex would not have long to gloat over his long awaited victory over his brother, as the arriving Weapon X impaled him from behind in retribution[13].
New Apocalypse
After Weapon X volunteered to become the new Apocalypse to spare the world from the Judgement of the Celestials, he started resurrecting formerly deceased mutants using energies from a Celestial Lifeseed. To his brothers ire, Alex Summers was among those successfully resurrected and was appointed the Minister of War.
It is of interest to note that it is established that Alex and Scott's powers do not effect each other, much like on Earth-616, however Alex was able to use his powers to slay Scott. Although his powers may not have had an effect on Scott in and of themselves, it is possible that a powerful impact resulting from the recoil from Alex's powers could have killed Scott.