Apocalypse

Real Name: En-Sabah Nur
First Appearance: X-Factor 5
Died In: X-Factor 68 and X-Force 18 (temporarily); X-Men Omega (permanently, but then, the entire time-line ended, so he never got a chance to ... ah, pull himself back together).

What's His Problem? Apocalypse believes in the survival of the fittest (thereby demonstrating his basic lack of understanding when it comes to evolutionary principles), and is not above engineering events to weed out the unfit. With the increasing frequency of super-powered beings on the planet, he sees no further use for plain ol' humans and does not factor them into his survivalist philosophy.
Powers: Variable, but mostly consisting of energy transmorgification and physical metamorphosis. After entering an alien space-craft, En Sabah Nur was forever altered into something beyond human, or even mutant. He now has utter control of his own molecules, can add to his mass and height at will, and possesses almost unlimited strength. That being said, he has trouble handling Cable, was beaten by Stryfe, and humiliated by Archangel when still weak from Stryfe's attack. His two deaths in this timeline didn't prevent Apocalypse and Cable from exchanging some harsh words during the Onslaught crisis.
Favorite Quote: "Threats. Consider me duly intimidated." (X-Factor 86, during the Executioner's Song cross-over.)
Heroes He Keeps Running Into: Although he first clashed with X-Factor, Cable is Apocalypse's primary foe. Cable was raised in an alternate future where Apocalypse ruled, and has come back in time several times to either confront Apocalypse or to maintain the timeline so that Apocalypse can never rise to power. Archangel, who owes his metal wings and his brooding nature to Apocalypse, cannot be trusted to behave himself when Poccy's around.
People Who Think He's Not So Bad: The Dark Riders (AKA the Horsemen), Apocalypse's band of mutant assassins that once included Archangel, believe in his survival of the fittest propaganda. Unfortunately that meant they promptly deserted him when Apocalypse was defeated by Cable's clone, Stryfe. During the Age of Apocalypse timeline (that's a web-site in itself!), Poccy was surrounded by "prelates" who carried out his orders, served by Mister Sinister, and had a devoted and homicidal son called Holocaust. Holocaust now exists in this timeline, but what the relationship is between him and his "father" has yet to be determined.
Most Despicable Act: The transformation of the Angel, Warren Worthington III, into the Archangel, herald of death and leader of Poccy's Horsemen of the Apocalypse. Turning one of the most well-adjusted of the mutant crowd into a brooding, near-murderous, metal-winged creature was a real shame. Warren has regained his feathered wings, but the damage done to the character may never be repaired.