The longer any movie series goes on, the higher the chance it will eventually retcon itself. And as one of the largest and most successful movie series of all time, the MCU is full of examples where newer movies retconned the older ones. Most often, they changed important details about known characters or certain events that transpired in the past.
While not all the retcons were accepted well by the fans, some MCU retcons hit the mark and were for the best. They also showed that the MCU continues to evolve as a fictional universe and isn't afraid of change, which means it can still surprise its fans!
6 Peter Parker And Tony Stark Met Years Ago
The official first meeting between Spider-Man and Iron Man happened in Captain America: Civil War (2016) when Tony Stark recruited Peter Parker to fight by his side. However, a fan theory soon emerged that the child in an Iron Mask that Iron Man saved in Iron Man 2 (2010) was none other than young Peter Parker.
This theory was later confirmed by none other than Jon Watts who directed all three Spider-Man solo movies. Tom Holland also supported the theory. It helps even better understand Peter's admiration of Tony Stark. The two superheroes went on to build a father-son relationship in the MCU and bringing Peter back was the main motivation why Stark invented time travel in the first place in Avengers: Endgame (2019).
5 Bruce Banner Changed His Face
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The Incredible Hulk (2008) is one of the most underappreciated MCU movies. And not because it's a bad movie but because it isn't as connected to the rest of the MCU. In the movie, Edward Norton played Bruce Banner, but the role was later recast and Mark Ruffalo took on the part. Despite Norton's solid performance in the movie, Ruffalo did an excellent job in the role and his Banner and Hulk became popular even though he never got a solo movie of his own.
Despite his angry green persona, Ruffalo brought kindness to the part that was mostly missing in Norton's darker, edgier performance. And seeing Hulk interact with the likes of Thor in Thor: Ragnarok (2017) or even confused Scott Lang in Avengers: Endgame made up for the change even more.
4 Phil Coulson Survived
One of the most unexpected moments in the first Avengers (2012) was Phil Coulson's death. Loki stabbed him with a spear, and Coulson's death helped reunite the Avengers who were previously arguing and didn't work as a team. As subsequent movies and most notably Agents of S.H.I.E.L.D. showed, Phil Coulson didn't die.
Instead, he returned to lead the team in Agents of S.H.I.E.L.D. and solve more than one superhero crisis. By bringing him back, the MCU got to show the fans even more corners of the universe, ones that the movies didn't have enough space and time for. What's more, Coulson went on to become one of the most popular characters. That's not a bad result for a character that was originally just a sidekick to Nick Fury.
3 The Mandarin Is Real...And He's Scary
The MCU took a long time before it introduced the real Mandarin. It also managed to retcon itself in a single movie. First, it looked like Ben Kingsley was playing the iconic villain. But he turned out to be a hired actor named Trevor Slattery. The main Iron Man 3 (2013) villain Aldrich Killian also wasn't the true Mandarin. His identity was revealed eight years later, in Shang-Chi and the Legend of the Ten Rings (2021) where Trevor Slattery made his reappearance.
The real Mandarin was an accomplished fighter who led his own criminal organization, the Ten Rings, and thanks to Tony Leung's performance, was much scarier than the other characters who stole his name for themselves. By introducing the real Mandarin, the MCU successfully retconned the notion that the Mandarin was just a boogeyman and not an actual person.
2 Tony Stark's Parents Didn't Die In An Accident
After Howard Stark helped create Captain America in Captain America: The First Avenger (2011), it was a bit anti-climatic to have him die in a car accident that was barely mentioned by Tony in the movies. Yet new information later revealed that Howard's and Maria's death was no accident. Instead, they were killed by the Winter Soldier, who was controlled by Hydra at that time. Howard Stark even recognized Bucky Barnes, but it did him no good as Bucky suffered from amnesia and he had no idea who Howard was.
The newfound information put Captain America in a difficult situation since he had to decide whether he would tell his friend Tony the truth or protect his even older friend, Bucky. Of course, Steve Rogers chose the latter, and it was one of the major aspects that led to the Civil War as well as the Avengers' subsequent defeat at the hands of Thanos. As such, this seemingly simple retcon had a large impact on multiple MCU movies.
1 Thor Freely Travels To Earth
After the destruction of the bridge Bifrost, the first Thor (2011) movie stated that Thor could no longer get to Earth now that the bridge was gone. That also meant Thor had to leave his girlfriend Jane Foster behind. Yet in the subsequent movies, Thor travels freely to Earth to help out the Avengers when they fight Loki, Ultron, as well as Thanos.
Seeing more of Thor is always excellent news, especially for all fans of the God of Thunder, so it's good that the MCU figured out a way how to bring Thor from Asgard to Earth. Even if it meant retconning its history a little.