According to ComicBook.com on Dec. 9, director Bryan Singer of "X-Men: Days of Future Past" has clarified on his Twitter account that Apocalypse of "X-Men: Apocalypse" is not an alien. Previous script end tease information from the film made it look like the villain was from another planet only because it fell from the sky, but comic lore indicates otherwise.
Singer had tweeted earlier today, “#Apocalypse is not an alien".
In the comic book, he is an ancient mutant in all actuality from Egypt and his given name is En Sabah Nur. As a child he was discovered orphaned by a nomadic group that took him in as their own. His powers had later come to be revealed when he and his nomadic family was enslaved, but was able to use his mutant powers to free himself.
Apocalypse main significance and role during that time was traveling around the world seeking out primitive cultures and posing as some kind of death god. He later had acquired a kind of technology that involved some regeneration chamber that would allow him to remain confined in stasis for long periods of time only to re-emerge even more powerful.
Some people may think that Apocalypse's encounter with Magneto could be attributed with the Egyptian mutants re-emergence into the future. But this only speculation.