The Age of Apocalypse was an event that occured within the universe of Marvel Comics. The event began with the Legion Quest saga which occurs in Uncanny X-Men 320-321 and X-Men 40-41. In Legion Quest, Professor Xavier's only child, Legion, awakens from the coma that he's been in for a long time. Legion is a very powerful mutant with his only flaw being that his multiple personalities seperated his abilities. But after his awakening, he's much more focused than he's ever been. Legion creates a plan in which he hopes to garner pride from his father, and complete what his father was never able to do. He decides to go back in time and kill his father's main adversary in the present: Magneto. Four of the X-Men chase after him and get transported back in time with him. All of them suffer a sort of time amnesia and by the time they remember their mission, so has Legion.
The X-Men attempt to stop Legion as he confronts Professor Xavier, Legion's future mother, and Erik Lensherr(better known as Magneto). Unfortunatly as Legion announces his intention to kill Magneto, Xavier throws himself in the way of Legion's energy blast and dies. From the death of this single man, the current X-Men team and Legion dissipate. Only Bishop, the mutant out of time continues on. The twenty years after Xavier's death were quite drastically different than if he had lived.
Starting in the February of 1995, the first issue of the Age of Apocalypse came out, X-Men Alpha. This special issue introduced the new world that the X-Men universe would exsist in for the next four months. America is a strange place, that long ago was taken over by the immortal Apocalypse. His creed of "Survival of the Fittest" had been greatly applied, and the normal human population has been reduced in a rather Holocaust-like manner. Many mutants slaughtered if their powers could be considered a threat to Apocalypse's reign. Apocalypse's few oppositions are Britain and a team of rag-tag mutants led by Magneto. In the twenty years since Xavier's death, Bishop has travelled the world and been searching for a solution. His mind half gone, he finally recovers upon seeing Magneto. With Magneto's special form of questioning, he learns of the way to put the world right. He sets different groups of mutants on near impossible missions for the better of the world, and entire universe.
Then in March, every X-title changed into an Age of Apocalypse title for four months. X-Man, the most powerful psychic, follows his own path. He is a key piece for he is the one that must stop Apocalypse. He was created in Mr. Sinister's labs from the DNA of Jean Gray and Cyclops. X-Calibre follows Kurt Darkholme, better known as Nightcrawler, and his mother, Raven Darkholme or Mystique, as they are sent to Avalon to recover the mutant prophet, Destiny. With Destiny, Magneto hopes to insure that Bishop's future is true. Generation Next gives us the mutants in training, being trained by the rather malevolent Kitty Pryde (Shadowcat) and Colossus. Magneto sends them on what seems to be a death mission, recover a single mutant from the slave mines. This mutant is Ilyana, Colossus's sister, who has the latent mutant abilities of time travel. The Astonishing X-Men were sent to stop a human culling by the horseman of Apocalypse, Holocaust. Weapon X is the mission of a sole man, Logan, as he tries to make sure that the British council will not decide to nuke America, with mutants and humans alike. If there's one man that can do the mission, it's Wolverine. Factor X is an odd one out of the bunch. Factor X belongs to Mr. Sinister, and in like thought is thought to be controlled by Apocalypse. This is as far as it can get from the truth. Sinister has been making sure that his group of mutants have been learning to be self-sufficient. With Sinister's vanishing, the team is left in disarray. Sinister's wish is for Cyclops to take up his place, and no one knows what this is supposed to accomplish. Gambit and the X-Ternals are sent for the most lucrative item of all, the M'kraan Crystal. The crystal is in a galaxy far away, and Gambit and his team are supposed to steal it. For it is yet another key to fixing reality. The Amazing X-Men are sent to help the Sentinels of the British council as they evacuate humans from America. During the mission they face problems from violent Sentinels, as well as the newest horseman of Apocalypse, Abyss. X-Universe tells the tales of the famous non-mutants from the Marvel universe, as they try to help the humans in America. There was also the single issue series The Age of Apocalypse: The Chosen, which covered more of the world events.
X-Men Omega told the end of the Age of Apocalypse. Bishop was returned back twenty years to stop Legion. Bishop used Legion's powers to show him that his plan would've failed and made the world worse. Legion's time powers broke down, and as Legion and the Age of Apocalypse Bishop disappeared into a time nexus the X-Men were returned to their proper time. Things returned to normal... for the most part. A few minor changes had occured, elaborated in X-Men Prime. Some of the greatest changes came from the four people who had survived from the Age of Apocalypse: the dark scientist of the pens, Beast; the favorite horseman of Apocalypse, Holocaust; the commander of the slave mines, the Sugar Man; and the artifically created psychic, Nate Gray.
There have been a few stories that have returned to the dark time of Apocalypse. Published in 1996 was Tales from the Age of Apocalypse: By the Light. Then in 1997 came Tales from the Age of Apocalypse: Sinister Bloodlines. The Age of Apocalypse also gave us a character from the Marvel Universe who had shortly died after her appearance, Blink. However, in the Age of Apocalypse she had survived. The issues that showed her created quite a large fanbase, with the fans demanding her reappearance. Marvel finally did obey the fans, and gave them the limited series Blink.
Series Changes:
Cable became X-Man - Writer: Jeph Loeb - Artist: Steve Skroce
Excalibur became X-Calibre - Writer: Warren Ellis - Artists: Ken Lashley(1,3-4), Roger Cruz and Renato Arlem(2)
Generation X became Generation Next - Writer: Scott Lobdell - Artist: Chris Bachalo
Uncanny X-Men became The Astonishing X-Men - Writers: Scott Lobdell and Jeph Loeb(3) - Artist: Joe Madureira
Wolverine became Weapon X - Writer: Larry Hama - Artist: Adam Kubert
X-Factor became Factor X - Writer: John Francis Moore - Artist: Steven Epting
X-Force became Gambit and the X-Ternals - Writer: Fabian Nicieza - Artists: Tony Daniel(1-2), Salvador Larocca(3-4)
X-Men became The Amazing X-Men - Writer: Fabain Nicieza - Artist: Andy Kubert
X-Men Unlimited became X-Universe - Writers: Scott Lobdell, Terry Kavanagh - Artist: Carlos Pacheco
Series Introduced Only for the Age of Apocalypse:
The Age of Apocalypse: The Chosen - Writer: Howard Mackie - Artist: Tom Lyle, Val Semeiks, Salvador Larocca, Tim Sale, Steve Skroce
Blink - Writers: Scott Lobdell, Judd Winnick(2-4) - Artists: Tyson McAdoo(1), Trevor McCarthy(2-4)
Tales from the Age of Apocalypse: By the Light - Writers: Scott Lobdell, Ralph Macchio - Artist: Joe Bennett
Tales from the Age of Apocalypse: Sinister Bloodlines - Writers: John Francis Moore, Brian K. Vaughan - Artists: Steven Epting, Nick Napolitano
X-Men Alpha - Writers: Scott Lobdell, Mark Waid - Artists: Steven Epting, Roger Cruz
X-Men Omega - Writers: Scott Lobdell, Mark Waid - Artists: Roger Cruz
Sources:
http://members.tripod.de/maelmill/AGEAPOCA.HTM
http://www.danger-room.net/cerebro/aoa.htm
http://www.geocities.com/SiliconValley/Park/6265/Imagine.html
http://www.chronology.net/default.pl/indexes