Apocalypse (En Sabah Nur) is a supervillain appearing in American comic books published by Marvel Comics. He is one of the world's first mutants, and was a principal villain for the original X-Factor team and later the X-Men and related spin-off teams. Created by writer Louise Simonson and artist Jackson Guice, Apocalypse first appeared, unnamed, in Marvel Graphic Novel #17 (July, 1985) and his full debut in X-Factor #5 (June 1986). Apocalypse is one of the most powerful beings in the Marvel Universe and the father of the original incarnation of the Horsemen of Apocalypse.

Since his introduction, the character has appeared in a number of X-Men titles, including spin-offs and several limited series. Apocalypse has also been featured in various forms of media, including a feature film where he was portrayed by Oscar Isaac in X-Men: Apocalypse.

While writing the first five issues of X-Factor, Bob Layton dropped hints of a villain operating behind the scenes and leading the Alliance of Evil (mentioned in X-Factor #4, May 1986). Layton intended to reveal this character to be the Daredevil villain the Owl on the final page of X-Factor #5. However, Layton left the book after writing this issue and was replaced by writer Louise Simonson. Editor Bob Harras said that the character arose because of storytelling needs: "All I had communicated to Louise was my desire that an A-level, first class character be introduced. I wanted a Magneto-level villain who would up the stakes and give the X-Factor team reason to exist."

In a 2011 interview with The Philadelphia Inquirer, Simonson explained that when the X-Factor series was created, the original five X-Men were pulled out of the purview of Chris Claremont, who was writing The Uncanny X-Men. However, Simonson felt that the series needed an archenemy, or what Simonson called "a big, bad villain", and conceived of Apocalypse. Simonson described the character thus:

When X-Factor was created, it caused a split in the "Mutant World" [and] several seminal characters were pulled out of [writer] Chris Claremont's X-Men. Apocalypse is the first mutant – a brilliant shape-shifter who is virtually immortal – and sees himself as the father of mutantkind. In his early years, which I covered in the X-Factor Forever miniseries... Apocalypse encountered the Celestials and realized there was a time when humanity might be judged unworthy and destroyed. Consequently, he's been using Darwinian principles – survival of the fittest – to kill off the weak and force the survivors to grow stronger, to push humanity to get better and more powerful. He considers himself the Apocalypse of modern man and the father of what humanity will come next – Mutantkind. Where Magneto sees mutants as the next step of evolution and strives to protect all mutants, Apocalypse believes in absolute survival of the fittest – so if the Hulk, for example, is stronger than [the X-Men's] Colossus... well, in Apocalypse's world he would say, 'Bye, bye, comrade.'

Harras also commented, "As soon as I saw the sketch by Walter [Simonson] and heard Louise's take on him, I knew we had the character I wanted. Jackson [Guice] redrew the page, patching in the shadowy Apocalypse where the Owl had been. But the genesis was clearly Walt and Weezie's." Guice admitted to difficulty recalling the details behind redrawing the last page of issue #5: "The best I can remember now is putting his look together pretty much right on the pencil page—just adding bits of costuming business which hinted toward his true appearance when we'd eventually see him in full reveal. I don't believe there was even a character sketch done for him at that point—I planned on making sense of it all later on, but by then I was gone and others had that concern." Apocalypse's silhouette in issue #5 does not match up with his full appearance in issue #6, suggesting the possibility that Guice was using Simonson's sketch as a reference for issue #6 but did not have access to it earlier, necessitating that he come up with his own design for issue #5. Walter Simonson himself has downplayed his role in the character's creation, saying that Guice was responsible for creating the design and that he, Simonson, merely modified it later: "I did not co-create Apocalypse. However, I wish I had. Louise Simonson and Jackson Guice created him. He appeared in a few panels at the end of one of Jackson’s last X-FACTORs, so I am the first artist to use him extensively in stories. And I kind of juiced up his physique a bit."

Bob Harras said on the character of Apocalypse:

He looked fantastic. Also, the name is dynamic. It tells you right off this character means trouble. And he came with a clear-cut agenda: 'survival of the fittest.' He didn't care if you were a mutant—if you were weak, you would be destroyed. He was merciless, but his philosophy was easy to grasp and it fit in with the harder edge of evolution which is part and parcel of the mutant story. Isn't that what humans fear about mutants? That they are the next step? Now, we had given mutants something new to fear: a character who would judge them on their genetic worthiness. [...] To his own mind he wasn't evil (despite his leadership of the Alliance of Evil, which I think we dropped pretty soon after Apocalypse's introduction); he believed he was doing the right thing. He was ensuring evolution. To me, he was the perfect next step in the mutant story.