Apocalypse is arguably the closest thing the X-Men have to a true nemesis. While the X-Men have traditionally protected a world of humans that hates and fears them, Apocalypse is dedicated to the idea of the survival of the fittest and would gladly crush anyone weaker than him under his feet. Stories like the fan-favorite Age of Apocalypse and Cable's dark future have even given readers first-hand looks at dystopian worlds under Apocalypse's ruthless rule.
However, Marvel has been showing a surprisingly noble side to Apocalypse lately. After Powers of X #4 added a new heroic chapter to his history, the longtime X-villain accepted Charles Xavier's request to join the X-Men on the mutant nation Krakoa.
With Apocalypse apparently set to join the mystical X-Men team Excalibur after House of X, En Sabh Nur is seemingly set to become a full-fledged hero. However, this heroic transformation isn't as sudden as it might seem at first glance.
As originally conceived by Louise Simonson, the core of Apocalypse's unforgiving philosophy isn't really evil. As Simonson told The Philadelphia Inquirer, the villain only embraced Darwinian ideas to ensure that the humans and mutants of Earth would be strong enough to survive the potential judgment of the Celestials, Marvel's all-powerful space gods.
While later stories twisted that motivation to make Apocalypse an agent of the Celestials, other stories established that En Sabah Nur wasn't inherently evil. In 2011's Uncanny X-Force #7, Rick Remender and Esad Ribic introduced a young clone of Apocalypse who was raised in a nurturing environment and came to be known as Genesis. Over the next decade, Genesis proved himself to be a true hero as he served on various X-Men teams.
When Genesis was sent hurtling back in time to Ancient Egypt, he even befriended a young Apocalypse in 2016's All-New X-Men #10, by Dennis Hallum and Mark Bagley. In that story, the young Apocalypse was described as "kind, thoughtful and generous to a fault."
Despite his better qualities, Nur's gray skin made him an outcast from normal society. Accordingly, he joined the Sandstormers, a band of ruthless wandering raiders who adhered to a strict "survival of the fittest" philosophy. Hardened by his upbringing, the young Apocalypse carried out a mission of vengeance against the relatively more villainous villainous Pharaoh Rama-Tut, who was secretly the time-traveling Kang, in Terry Kavanagh and Adam Pollina's Rise of Apocalypse miniseries.
In what's still arguably Nur's most heroic deed, Hickman and Dustin Weaver's S.H.I.E.L.D. #1 saw Apocalypse help the earliest incarnation of S.H.I.E.L.D. and Marvel's other ancient heroes push back an invasion of Brood aliens. This moment was even deemed important enough to be chronicled in the ongoing Mark Waid and Javier Rodriguez's History of the Marvel Universe.
Even once Apocalypse was soon well on his way to becoming a would-be world conqueror, he still took time for the occasional semi-heroic deed like going to war with Dracula in Frank Tieri and Clayton Henry's aptly-titled X-Men: Apocalypse vs. Dracula.
While Apocalypse spent the next several centuries becoming one of Marvel's most vicious villains, Powers of X revealed some more of Apocalypse's previously unmentioned heroic deeds.
At some point in the ancient past, Apocalypse defeated a group of demonic invaders who cut the Okkara land mass in two, which led to the creation of Krakoa. That's why Krakoa greeted Apocalypse so warmly when he accepted Xavier's invitation in House of X #5.
In Moira MacTaggert's ninth life, she and Apocalypse founded the X-Men and shepherded mutants as a whole for over a century. While that timeline ultimately didn't end well, he and Moira formulated a plan for her next life that has seemingly been successful in stopping the creation of one of the X-Men's most powerful foes.
While it's still not clear what role Apocalypse will play in the final act of House of X, he's already pledged his allegiance to Xavier and has been billed as a member of Excalibur in multiple upcoming issues.
Despite his recent history of good deeds, Apocalypse is still one of the most lethal figures in the Marvel Universe, and he could reasonably be described as the X-Men's most villainous recruit ever. Even though the X-Men have a most successful history of turning enemies like Rogue, Emma Frost, Magneto and Mystique into teammates, Apocalypse has always stood apart from other villains as a singular threat. However, now Apocalypse is just another citizen in Xavier's nation.