En Sabah Nur, later known as Apocalypse, was born in the harsh, unforgiving desert of ancient Egypt, ruled by Rama-Tut, a band of nomadic raiders found an infant, gray-skinned and freakish in appearance, abandoned by the settlers of Akkaba. The nomads took the child for their own, giving him the name En Sabah Nur, “The First One,” and teaching him to be strong in order to survive the desert as a child. This idea, that "the strong will survive," would shape Apocalypse's actions throughout time. He soon found that he had mutant abilities, leading him to believe himself "strong" and blessed. En Sabah Nur soon discovered Rama Tut’s Celestial technology underneath Egypt, and then destroyed the Egyptian rulers around him and twisted Ozymandias into the being he is today. Apocalypse would use his newfound technology to "regenerate" for long periods of time, becoming more and more powerful when awakening.
Ever since then, Apocalypse has been a major antagonist of the Marvel universe, his goals of a world where only the strong survive under his rule being thwarted by many a hero.
He has full control of the molecules of his body, giving himself the ability to replicate almost any superhuman abilities. For example, he has changed his size, he has become extremely malleable and flexible, enhanced his physical abilities, transformed his limbs into guns/wings/jets, adapted his body to apparently any disease or hostile environment, and given himself virtually any physical superhuman power.