One of the more intriguing Marvel Comics crossover events in recent years was 2014's Original Sin, by Jason Aaron and Mike Deodato, Jr. The event kicked off with the brutal murder of Uatu, the Watcher and the theft of his all-seeing eyes. As the heroes of the Marvel Universe launched an extensive investigation to find his killer, their greatest secrets -- including some completely unknown to anyone prior to the event -- were brought to the surface, where they dramatically changed the heroes' status quo.
By the end of the event, the heroes discovered the Watcher's murderer was one of their own, and the Avengers would be fractured once again by the deep, dark secrets brought irreversibly into the light. Here's how Earth's Mightiest Heroes were each changed by the event.
CAPTAIN AMERICA
After overthrowing Norman Osborn and his Dark Avengers at the end of the crossover event Siege, a new iteration of the Illuminati formed to secretly steer the course of superhero interests throughout the Marvel Universe. Captain America was initially part of this new lineup to provide a strong moral voice to the proceedings. This would prove to be his undoing when the Illuminati learned that alternate worlds across the Marvel Multiverse were colliding in timed events known as "incursions." Captain America wanted to pursue peaceful means to prevent incursions but was overruled and had his mind wiped of the incursions and Illuminati's existence to prevent his interference with their dark agenda.
Original Sin restored Steve Rogers' memories of the Illuminati, the incursions, and the mindwipe led by Iron Man. The Avengers would fracture once again, with Captain America pursuing Iron Man while the latter continued to destroy incursions by any means necessary, regardless of the collateral damage involved to preserve the Marvel Universe setting up their roles leading into Secret Wars.
IRON MAN & HULK
Captain America wasn't the only Avenger who had a grudge with Iron Man after having his memories restored, as the Hulk similarly learned an old secret that Tony had harbored for years. The gamma radiation bomb that had first transformed Bruce Banner into the Jade Giant was developed by Stark Industries when the company was still primarily involved in arms manufacturing. To make matters worse, the bomb's explosion was apparently caused by tinkering caused by Tony while he was in a drunken stupor at the time.
An angry Hulk attacks Iron Man, and even Tony's latest Hulkbuster armor was unable to stop the Green Goliath's fury. However, Tony was able to eventually talk the Hulk down, revealing that his last-minute modifications actually prevented the gamma radiation from killing Bruce and affecting innocent bystanders nearby. Satisfied with this answer, the Hulk ceases his attack and moves on, aware that Tony had also sent Bruce an email warning him of the radiation's transformative properties that Bruce had ignored years ago in his own hubris.
THOR & ANGELA
Thor and Loki learned that Odin had secretly fathered a daughter raised on Heven, the hidden Tenth Realm, who grew up to be the Guardians of the Galaxy's Angela. Following a war between Asgard and the Tenth Realm, Odin severed Heven from the remaining Nine Realms and erased everyone's memory of its existence.
Heven and Angela had since been restored by the reality-altering events of Age of Ultron, with Thor and Angela dueling one another as a renewed war between Heven and Asgard loomed. After learning Thor was her brother, Angela was exiled from Heven while the war was called off. Despite being welcomed by Odin, Angela decided to take the opportunity to explore the other realms.
SPIDER-MAN & SILK
For years, Spider-Man had assumed he was the only person who had been bitten by the radioactive spider that gave him his superpowers. Peter Parker was shocked to learn during Original Sin that his high school classmate Cindy Moon had similarly been bitten and given superpowers of her own. But instead of becoming a costumed hero, Spider-Man's mystical mentor Ezekiel confined Cindy to a secret bunker immediately afterward and separated her from her family to keep her safe from Morlun.
Upon her release from the bunker as an adult, Cindy became the superhero Silk and helped thwart an attack by the Black Cat and Electro. While searching for her missing family, Silk found herself inextricably linked with Spider-Man due to their shared, totemic power source, going on to distance herself from him while joining the latest incarnation of the Agents of Atlas.
NICK FURY
The biggest twist in Original Sin involved the true role of the original Nick Fury, the longtime S.H.I.E.L.D. director. Fury was revealed to have been the killer of the Watcher all along, murdering Uatu for withholding information that was vital to Fury's secret ongoing mission to defend the Earth from extraterrestrial threats and obtaining the necessary information stored within his eyes.
With his Infinity Formula failing him, Fury began to dramatically age and replaced Uatu as the new Unseen Watcher while Bucky Barnes became the new hero to secretly defend Earth from extraterrestrial enemies for a time.