Apocalypse (X-Men: Evolution)

En Sabah Nur, better known as Apocalypse, is an ancient and very powerful mutant who has been revived to take control of the world.

Biography
En Sabah Nur was born in Egypt with grey skin and bizarre blue patterns on his skin. He was abandoned to die in the desert. His cries were heard when he was found by a tribe of bandits led by a fierce warrior named Baal. Baal saw the potential in the infant and trained him to be a great warrior. Baal's training combined with En Sabah Nur's mostly dormant mutant abbilities made him untouchable in battle.

The Pharaoh Rama-Tut soon heard of En Sabah Nur's inhuman power and sent his army to slay the boy. The pharoh's army massacred the bandits and killed Baal. Upon seeing the death of the closest thing he had to a father, En Sabah Nur's full powers emerged and he desimated the Pharaoh's army with his raw power before heading off to find the Pharaoh.

En Sabah Nur had discovered a device left by Rama-Tut called the Eye of Ages that would turn all humans on Earth into mutants. When En Sabah Nur tried to power the device, he was weakened. His high priests, afraid of his power, imprisoned him in the Eye of Ages then took him to the top of the Himalayan Mountains to be imprisoned him behind three doors. He became known by the name Apocalypse.

Centuries later, Apocalypse used his telepathy to reach the world outside his prison and found the hypnotist Mesmero. Mesmero used his abilities to manipulate Jean Grey alog with several other X-Men to steal the first key. When Charles Xavier tired to break Mesmero's hold on Jean and the others Apocalypse intervened through Mesmero with a telekenetic blast. Though unaware of the identity of his attacker Xavier noted it was a mind more powerful than he had encountered before.

The final door required Mesmero to enlist the aid of Rogue and Mystique. Rogue used her absorbing power to absorb enough energy from other mutants to revive Apocalypse. Mystique used her shape-shifting abilities to unlock the door and was turned to stone in the process.

The X-Men and Magneto with his Brotherhood of Mutants and Acolytes worked together to stop Mesmero, but they were too late. The awakened Apocalypse defeated them all in an instant and vanished.

Apocalypse's master plan included uncovering pyramids in Mexico, China, and Egypt that would help relay the Eye of Ages' mutation affect across the globe. To help protect these pyramids, Apocalypse enslaved Magneto, Xavier, Storm, and Mystique as the Four Horsemen of Apocalypse to guard the pyramids and the base hidden under the Sphinx.

The X-Men gathered their allies such as modified Sentinels under the command of S.H.I.E.L.D.. Together they launched an offensive against the pyramids. In the end, Rogue stopped Apocalypse by using the power she absorbed from Leechto shut of his mutant abilities and trap him in the Eye of Ages. Wolverine then sent Apocalypse through time using the vessel that Rama-Tut had used to arrive in ancient Egypt. Apocalypse was not killed, but his destination was unknown. After the battle, Wolverine and Rogue thought they may not be lucky to see the last of Apocalypse. Xavier read his mind and saw various visions of the future.

Powers and Abilities
As the first known mutant and, perhaps, the most powerful one, Apocalypse possesses several abilities beyond the ones possessed by other mutants. He possessed psychic abilities that were stronger than Charles Xavier's, Jean Grey, etc., energy manipulation, force field generation, invulnerability, shape-shifting, molecular manipulation, absorption and many others.

While it's not exactly confirmed or denied, this version of Apocalypse may very well be immortal, as he was preserved within the Eye of Ages, or this preservation was a function of the Eye itself.

Baal
Apocalypse, back when he was known as En Sabah Nur, was found as an infant by a tribe led by Baal. The leader took him in and raised him as his son. Baal saw the potential of En Sabah Nur and was the closest thing to an actual father to him. His death caused Nur's dormant powers to manifest and from then on and Nur became Apocalypse.

Rama-Tut
As the driving force behind the slaughter of the tribe Apocalypse grew up in, Rama-Tut is the enemy most despised by the mutant for the death of his surrogate father. When Apocalypse tried to do away with the pharaoh, Rama-Tut escaped through time. He left his technology behind, which Apocalypse claimed for himself including the Eye of Ages.

Background
Apocalypse was voiced by David Kaye, who also voiced Charles Xavier.

The producers stated that had the series continued on for another season Apocalypse would have returned.

In the Comics
At one point he merged with Cyclops.