Pharaoh Apocalypse, is the ruler of Egypt and the worlds first mutant he has many abilities and has lived for centuries but, the body he currently inhabits has become old and weak. The mutant king has his followers, the Horsemen of Apocalypse set up the grand ceremony in his pyramid, so he can transfer his consciousness into a new mutant host body and continue his immortal reign. All the citizens and slaves are forced to attend and watch him ascend into power once more. Unknown to him but, some of his subjects no longer want to suffer under his tyranny and have formed a rebellion against him.
Apocalypse ends up entombed for thousands of years and mutants continue to spread across the globe. Apocalypse is nearly forgotten from history except by certain cults who long to awaken him again. In the original timeline, Apocalypse seemingly was never awakened even during the War of the Sentinels. However, the rift in time caused by the events of X-Men: Days of Future Past ultimately caused him to eventually brought back to life by the actions of Moira MacTaggert in the 1980s.