Since Iron Man first introduced audiences to Tony Stark (Robert Downey Jr) and his exceptional facial hair, the Marvel Cinematic Universe has grown exponentially. In the last year alone, Shang-Chi (Simu Liu) was recruited by Wong to uncover the mystery of the ten rings, a celestial crawled out of the earth, and three Spider-Men shared the screen in the record-breaking Spider-Man: No Way Home.

Related: From Kano to Green Goblin, the Best Movie Villains of 2021That's not to say it's been all sunsets and rainbows for the heroes of the MCU, though; many have laid down their lives while fighting to protect the earth and all those who live there. Every death is sad, but some are harder to forget than others. After all, most of the Avengers didn't even get the chance to say "goodbye" to Natasha. We're not crying; you are.

Quicksilver - Avengers: Age Of Ultron

Aaron Taylor Johnson and Elizabeth Olsen in Avengers: Age of Ultron
Image via Marvel

Many fans were left confused, upset, and a little disappointed when Pietro Maximoff (Aaron Taylor-Johnson) was left riddled with bullets after using his super-speed to save Hawkeye (Jeremy Renner). After all, it was Quicksilver's first appearance in the MCU, and many found it strange that Marvel would kill off a fan-favorite character without ever letting audiences get to know him.

One Reddit user went a step further, claiming that "Quicksilver's death is the biggest mistake in the MCU." Though the character made a brief pseudo-comeback in WandaVision, he was ultimately revealed to be an actor with little resemblance to the "real" Pietro. Given the character's limited screen time, the saddest thing about Quicksilver's death is seeing what it did to his sister, Wanda (Elizabeth Olsen).

Agent Coulson - The Avengers

Clark Gregg on the phone in Agents of Shield
Image via ABC

Agent Coulson (Clark Gregg) was a staple of Phase One, appearing in four of the five films and playing an integral role in the founding of The Avengers. Unfortunately, Coulson did not live to see Phase Two (depending on whether you consider Agents Of S.H.I.E.L.D. canon). He was fatally stabbed after trying to prevent Loki (Tom Hiddleston) from escaping the helicarrier.

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Thankfully though, his death wasn't for nothing as it united the team, giving them something to fight for. Coulson's death wasn't particularly traumatic for fans though, as a Reddit user commented, his death "was dramatic, but not big enough of a character for me to really care."

Killmonger - Black Panther

Black Panther T'Challa stares down Erik Killmonger

Though it may be surprising to find a villain on this list, Killmonger's (Michael B Jordan) death at the hands of his cousin T'Challa (Chadwick Boseman) left many MCU fans feeling blue. Yet, Killmonger was a hugely sympathetic character.

After experiencing an enormously traumatic childhood, he fought to share Wakanda's weapons and technology, hoping to empower Black communities around the world. Jordan's performance was exceptional, providing the perfect antagonist to Black Panther. It's no surprise multiple Reddit users voted for him in this Reddit thread asking who the MCU's saddest death was.

Aunt May - Spider-Man: No Way Home

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Image via Sony

Eyebrows were raised when Marisa Tomei was cast as Aunt May in the MCU's Spider-Man reboot, given that she's considerably younger than the character in the comics. Fans grew to love the character across Tom Holland's Spider-Man trilogy, though, and there weren't many fans unaffected by her brutal death at the hands of the Green Goblin (Willem Dafoe).

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While her death really tugged on our heartstrings, fans accept that she had to die for Peter to understand the sacrifices heroes must make. One Reddit user summed up the importance of her death because she died "defending her belief that the villains brought in by Doctor Strange could be saved."

Loki - Avengers: Infinity War

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Image via Marvel Studios

After years of building up Thanos as the MCU's big bad, the opening minutes of Avengers: Infinity War needed something drastic to show audiences the brutality of the Mad Titan. Unfortunately for the Prince Of Mischief, he found himself on the end of Thanos' wrath, unable to do anything as he choked him to death in front of Thor.

Of course, this isn't the first time Loki has 'died' in the MCU, and a past iteration of the character is currently alive and kicking in his own Disney+ show. That being said, the iteration of the character we all knew and loved does seem to be gone now, prompting many Reddit users to vote for him in this saddest MCU death thread.

Yondu - Guardians of the Galaxy Vol. 2

Image of Peter and Yondu from Guardians of the Galaxy 2

Yondu's (Michael Rooker) redemptive character arc in Guardians of the Galaxy Vol. 2 is easily the funniest, most surprising aspect of the beloved sequel. Though they spend the majority of the two films bickering and betraying one another, it's revealed that Yondu actually saved Peter Quill (Chris Pratt) from Ego (Kurt Russell) and has spent the years since looking after the person he considers a son.

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He continued looking after Peter right to the very end, sacrificing himself to ensure Quill escaped the wreckage of Ego's planet safely. James Gunn's music choice plays a significant role in Yondu's touching death, as pointed out by a Reddit user in this thread.

Groot - Guardians of the Galaxy

Groot in Guardians of the Galaxy

Never before in the history of cinema have audiences been so profoundly affected by the death of a giant sentient tree whose vocabulary is limited to just three words: "I am Groot." Much like Yondu, Groot (Vin Diesel) dies protecting his chosen family.

Groot and Rocket Raccoon (Bradley Cooper) have one of the best friendships in the entire MCU. In fact, it's Rocket's reaction to the death of his best friend that breaks audiences' hearts, as highlighted in this Reddit thread. Let's be honest, it's hard to think of a more heart-wrenching image than Rocket holding onto a twig that used to belong to his best friend.

Black Widow - Avengers: Endgame

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Image via Disney

When Black Widow (Scarlett Johansson) and Hawkeye (Jeremy Renner) traveled to Vormir to retrieve the soul stone, they were unaware of the sacrifice required to obtain the infinity stone. Given their intense, unwavering friendship the two fight, desperately trying to sacrifice themselves to ensure their best friend lives on.

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As was often the case, Natasha wins the fight and falls to her death, ensuring Hawkeye could return the soul stone to the modern day, so The Avengers can bring back everybody lost in the blip. A Reddit user thinks her death could have been avoided though, as explained in this eye-opening thread.

Vision - Avengers Infinity War

Paul Bettany and Elizabeth Olsen in Avengers: Infinity War
Image via Walt Disney Studios Motion Pictures

Avengers: Infinity War is relentlessly cruel to Wanda Maximoff. After spending the entire film trying to develop an alternative solution, Wanda and the rest of the Avengers finally accept that they need to destroy the stone in Vision's (Paul Bettany) head to stop Thanos. To make things even worse for the Scarlett Witch, she is the only person capable of doing so.

With Thanos approaching and no time to spare, Wanda is forced to destroy the person she loves more than anything else. In one final twist, Thanos uses the time stone to bring Vision back only to rip the infinity stone from his head, right in front of Wanda. One Reddit user managed to make the scene even sadder by posting a thread that provided proof that Vision was crying during the scene, something that should be impossible given he's a machine.

Tony Stark - Avengers: Endgame

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Image Via Marvel Studios

Despite years passing since the release of Avengers: Endgame, some fans are still not over Iron Man's death, as made evident in this Reddit post. Tony died as he lived, making sure he got the last word. The actor's improvised "I am Iron Man" line at the climax of Iron Man was already iconic, but repeating it before snapping his fingers and finally killing Thanos ensured that the four words will forever live on in cinematic history.

Despite his perfect family and delightfully cute daughter, Tony simply cannot rest knowing that he and the rest of the Avengers failed, allowing half of all life to be snapped away by the Mad Titan. After the returned Doctor Strange (Benedict Cumberbatch) finally confirms that this is the one chance the Avengers have to defeat Thanos, Tony makes the ultimate sacrifice to keep the earth safe, laying down his life so that everybody else can live on. Tony, we love you three thousand.

NEXT: 5 Spoiler Heavy Lessons That Spider-Man Learned In 'No Way Home'