In 1995, the world of the X-Men was consumed by the Age of Apocalypse, a massive crossover event that created one of the most iconic and enduring alternate realities in Marvel's history. In a timeline where Charles Xavier died before he could ever form the X-Men, the mutant Apocalypse turned most of the world into a living hell.
While the original "Age of Apocalypse" storyline is very much an X-Men story at its core, many other Marvel heroes made appearances or are name-dropped throughout the event, including several major Avengers. While all of Marvel's mightiest heroes played smaller roles than their mutant counterparts did, many of them met tragic fates in the" Age of Apocalypse" timeline.
SCARLET WITCH
Without Xavier, Magneto formed the X-Men in the Age of Apocalypse, and two of his first recruits were the Maximoff twins. Both Wanda and Pietro are founding members of their father's X-Men team and are much closer to him.
When the team leaves for it's first mission against Apocalypse, Wanda stayed behind to defend their Wundagore Mountain base and the many young or inexperienced mutants that live there. Tragically, the base is attacked by Apocalypse's sadistic son Holocaust, and Wanda is killed fighting him in Howard Mackie, Terry Dodson and Klaus Janson's X-Men Chronicles #1.
QUICKSILVER
Pietro Maximoff was an important member of the X-Men from a young age, and was very close to his father and sister. After Wanda's death, he became depressed and reckless during missions, only changing his behavior after endangering his team members. Pietro's close friendship with Storm also helped, and as years passed they began to fall in love.
Quicksilver was one of the main characters in Fabian Nicieza and Andy Kubert's Amazing X-Men, and he fought alongside his father until his demise in X-Men: Age of Apocalypse #6, by C.B. Cebulski and Chris Bachalo.
CAROL DANVERS
Although this Carol Danvers never received the powers of Captain Marvel in this world, her army experience made her a valuable asset to the Human Resistance League as the primary guard of their mutant ally Gateway, whose teleportation powers were crucial to their cause. She was brought into the Age of Apocalypse by Larry Hama and Adam Kubert's Weapon X #3, where she teamed up with her old army pal Logan to get Gateway's help transporting nuclear bombs for one last desperate strike against Apocalypse. However, Carol is captured by Donald Pierce and turned into one of his cybernetic Reavers.
Carol and the Reavers attacked the League's base and once again tried to kill Gateway. Forced to fight his friend, Weapon X tried to snap Carol out of her brainwashing. Just as it began to work Pierce sensed the change and killed her, though she was avenged almost instantly by Weapon X's claws.
IRON MAN
After injuring his heart attempting to sabotage Apocalypse's forces, Anthony Stark became an operative for the Human High Council. After being introduced in Scott Lobdell and Carlos Pacheco's X-Universe #1, he traveled to Wakanda to deliver humanitarian aid to the populace and get the help of Dr. Donald Blake and his assistant Gwen Stacy in investigating the former Horseman Mikhail Rasputin, who had supposedly deserted Apocalypse to help the human resistance.
After they walked into the obvious trap, Rasputin imprisoned them, but saw Stark's mechanical heart and decided to cybernetically enhance and enslave him. Stark and the League had sensed this possibility and turned his heart into an EMP booby trap that could shut down Rasputin's ship mid-operation. After being revived by Blake, Stark and the other prisoners took over the ship and began using it to transport human refugees.
HAWKEYE
Clint Barton briefly appeared in Scott Lobdell and Carlos Pacheco's X-Universe as a pilot for the Human Resistance League. He was in charge of Stark's mission to Wakanda, where they recovered Donald Blake, the human who became Thor's alter ego in the Marvel Universe.
Along with Gwen Stacy, he killed the Age of Apocalypse's Marauders, that world's version of Kingpin, Norman Osborn, Arcade and the Owl. After he was later captured, this Hawkeye helped with the prison breakout on Rasputin's ship too.
BRUCE BANNER
After debuting in Scott Lobdell and Carlos Pacheco's X-Universe #1, BruceBanner worked as a scientist for the Human Resistance League, but he was secretly a double agent, who was helping Rasputin sabotage their plans in exchange for resources that transformed him into a Hulk-like monster ironically called "The Thing."
As part of the group investigating Rasputin, he used his Thing form to attack the others, but revealed his true identity and helped his fellow humans escape from Europe. After still getting caught in the blast, Banner returned to Earth, where he forgot his ability to transform and lived in Apocalypse's slave pens before retiring to a small house full of scientific books. After Wolverine took control of the Age of Apocalypse and was corrupted into becoming Weapon Omega, Banner was dragged back into action before he was ultimately killed by Wolverine in David Lapham, Roberto de la Torre, and Renato Arlem's Age of Apocalypse #4.